Previous Issue

Table of Contents

Polymers, Volume 10, Issue 5 (May 2018)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-93
Export citation of selected articles as:

Research

Jump to: Review

Open AccessCommunication Novel Ultrafine Fibrous Poly(tetrafluoroethylene) Hollow Fiber Membrane Fabricated by Electrospinning
Polymers 2018, 10(5), 464; https://doi.org/10.3390/polym10050464
Received: 14 March 2018 / Revised: 10 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
PDF Full-text (2196 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Novel poly(tetrafluoroethylene) (PTFE) hollow fiber membranes were successfully fabricated by electrospinning, with ultrafine fibrous PTFE membranes as separation layers, while a porous glassfiber braided tube served as the supporting matrix. During this process, PTFE/poly(vinylalcohol) (PVA) ultrafine fibrous membranes were electrospun while covering the
[...] Read more.
Novel poly(tetrafluoroethylene) (PTFE) hollow fiber membranes were successfully fabricated by electrospinning, with ultrafine fibrous PTFE membranes as separation layers, while a porous glassfiber braided tube served as the supporting matrix. During this process, PTFE/poly(vinylalcohol) (PVA) ultrafine fibrous membranes were electrospun while covering the porous glassfiber braided tube; then, the nascent PTFE/PVA hollow fiber membrane was obtained. In the following sintering process, the spinning carrier PVA decomposed; meanwhile, the ultrafine fibrous PTFE membrane shrank inward so as to further integrate with the supporting matrix. Therefore, the ultrafine fibrous PTFE membranes had excellent interface bonding strength with the supporting matrix. Moreover, the obtained ultrafine fibrous PTFE hollow fiber membrane exhibited superior performances in terms of strong hydrophobicity (CA > 140°), high porosity (>70%), and sharp pore size distribution. The comprehensive properties indicated that the ultrafine fibrous PTFE hollow fiber membranes could have potentially useful applications in membrane contactors (MC), especially membrane distillation (MD) in harsh water environments. Full article
(This article belongs to the Special Issue Hollow Fiber)
Figures

Graphical abstract

Open AccessArticle Numerical Analysis of H-PDLC Using the Split-Field Finite-Difference Time-Domain Method
Polymers 2018, 10(5), 465; https://doi.org/10.3390/polym10050465
Received: 4 April 2018 / Revised: 19 April 2018 / Accepted: 23 April 2018 / Published: 24 April 2018
PDF Full-text (12967 KB) | HTML Full-text | XML Full-text
Abstract
In this work, an accurate numerical modeling of the diffraction properties of transmission holographic polymer dispersed liquid crystal (H-PDLC) gratings is presented. The method considers ellipsoid geometry-based liquid crystal (LC) droplets with random properties regarding size and location across the H-PLDC layer and
[...] Read more.
In this work, an accurate numerical modeling of the diffraction properties of transmission holographic polymer dispersed liquid crystal (H-PDLC) gratings is presented. The method considers ellipsoid geometry-based liquid crystal (LC) droplets with random properties regarding size and location across the H-PLDC layer and also the non-homogeneous orientation of the LC director within the droplet. The direction of the LC director inside the droplets can be varied to reproduce the effects of the external voltage applied in H-PDLC-based gratings. From the LC director distribution in the droplet, the permittivity tensor is defined, which establishes the optical anisotropy of the media, and it is used for numerically solving the light propagation through the system. In this work, the split-field finite-difference time-domain method (SF-FDTD) is applied. This method is suited for accurately analyzing periodic media, and it considers spatial and time discretisation of Maxwell’s equations. The scheme proposed here is used to investigate the influence on the diffraction properties of H-PDLC as a function of the droplets size and the bulk fraction of LC dispersed material. Full article
(This article belongs to the Special Issue Holographic Materials and Photonic Applications)
Figures

Figure 1

Open AccessArticle Chitosan Composites Synthesized Using Acetic Acid and Tetraethylorthosilicate Respond Differently to Methylene Blue Adsorption
Polymers 2018, 10(5), 466; https://doi.org/10.3390/polym10050466
Received: 20 February 2018 / Revised: 22 March 2018 / Accepted: 11 April 2018 / Published: 24 April 2018
PDF Full-text (1529 KB) | HTML Full-text | XML Full-text
Abstract
The sol-gel and cross-linking processes have been used by researchers to synthesize silica-based nanostructures and optimize their size and morphology by changing either the material or the synthesis conditions. However, the influence of the silica nanostructures on the overall physicochemical and mechanistic properties
[...] Read more.
The sol-gel and cross-linking processes have been used by researchers to synthesize silica-based nanostructures and optimize their size and morphology by changing either the material or the synthesis conditions. However, the influence of the silica nanostructures on the overall physicochemical and mechanistic properties of organic biopolymers such as chitosan has received limited attention. The present study used a one-step synthetic method to obtain chitosan composites to monitor the uptake and release of a basic cationic dye (methylene blue) at two different pH values. Firstly, the composites were synthesized and characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) to ascertain their chemical identity. Adsorption studies were conducted suing methylene blue and these studies revealed that Acetic Acid-Chitosan (AA-CHI), Tetraethylorthosilicate-Chitosan (TEOS-CHI), Acetic Acid-Tetraethylorthosilicate-Chitosan (AA-TEOS-CHI), and Acetic Acid-Chitosan-Tetraethylorthosilicate (AA-CHI-TEOS) had comparatively lower percentage adsorbances in acidic media after 40 h, with AA-CHI adsorbing most of the methylene blue dye. In contrast, these materials recorded higher percentage adsorbances of methylene blue in the basic media. The release profiles of these composites were fitted with an exponential model. The R-squared values obtained indicated that the AA-CHI at pH ~ 2.6 and AA-TEOS-CHI at pH ~ 7.2 of methylene blue had steady and consistent release profiles. The release mechanisms were analyzed using Korsmeyer-Peppas and Hixson-Crowell models. It was deduced that the release profiles of the majority of the synthesized chitosan beads were influenced by the conformational or surface area changes of the methylene blue. This was justified by the higher correlation coefficient or Pearson’s R values (R ≥ 0.5) computed from the Hixson-Crowell model. The results from this study showed that two of the novel materials comprising acetic acid-chitosan and a combination of equimolar ratios of acetic acid-TEOS-chitosan could be useful pH-sensitive probes for various biomedical applications, whereas the other materials involving the two-step synthesis could be found useful in environmental remediation of toxic materials. Full article
(This article belongs to the Special Issue Advances in Chitin/Chitosan Characterization and Applications)
Figures

Figure 1

Open AccessArticle Thermal Study of Polyols for the Technological Application as Plasticizers in Food Industry
Polymers 2018, 10(5), 467; https://doi.org/10.3390/polym10050467
Received: 12 April 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
PDF Full-text (2502 KB) | HTML Full-text | XML Full-text
Abstract
In this work is presented the complete thermal analysis of polyols by direct methods such as simultaneous thermogravimetric and differential thermal analyzer (TGA-DTA), differential scanning calorimetry (DSC), modulated DSC (MDSC), and supercooling MDSC. The different thermal events in the temperature range of 113–553
[...] Read more.
In this work is presented the complete thermal analysis of polyols by direct methods such as simultaneous thermogravimetric and differential thermal analyzer (TGA-DTA), differential scanning calorimetry (DSC), modulated DSC (MDSC), and supercooling MDSC. The different thermal events in the temperature range of 113–553 K were identified for glycerol (GL), ethylene glycol (EG), and propylene glycol (PG). Boiling temperature (TB) decreased as GL > EG > PG, but increased with the heating rate. GL showed a complex thermal event at 191–199 K, identified as the glass transition temperature (Tg) and devitrification temperature (Tdv), and a liquid–liquid transition (TL-L) at 215–221 K was identified as the supercooling temperature. EG showed several thermal events such as Tg and Tdv at 154 K, crystallization temperature (Tc) at 175 K, and melting temperature (Tm) at 255 K. PG also showed a complex thermal event (Tg and Tdv) at 167 K, a second devitrification at 193 K, and TL-L at 245 K. For PG, crystallization was not observed, indicating that, during the cooling, the liquid remained as an amorphous solid. Full article
(This article belongs to the Special Issue Thermal Properties and Applications of Polymers)
Figures

Graphical abstract

Open AccessArticle Column-Free Purification Methods for Recombinant Proteins Using Self-Cleaving Aggregating Tags
Polymers 2018, 10(5), 468; https://doi.org/10.3390/polym10050468
Received: 6 March 2018 / Revised: 18 April 2018 / Accepted: 20 April 2018 / Published: 25 April 2018
PDF Full-text (1881 KB) | HTML Full-text | XML Full-text
Abstract
Conventional column chromatography processes to purify recombinant proteins are associated with high production costs and slow volumetric throughput at both laboratory and large scale. Non-chromatographic purifications based on selective aggregating tags have the potential to reduce costs with acceptable protein yields. A significant
[...] Read more.
Conventional column chromatography processes to purify recombinant proteins are associated with high production costs and slow volumetric throughput at both laboratory and large scale. Non-chromatographic purifications based on selective aggregating tags have the potential to reduce costs with acceptable protein yields. A significant drawback, however, is that current proteolytic approaches for post-purification tag removal after are expensive and non-scalable. To address this problem, we have developed two non-chromatographic purification strategies that use either the elastin-like polypeptide (ELP) tag or the β-roll tag (BRT17) in combination with an engineered split intein for tag removal. The use of the split intein eliminates premature cleavage during expression and provides controlled cleavage under mild conditions after purification. These self-cleaving aggregating tags were used to efficiently purify β-lactamase (β-lac), super-folder green fluorescent protein (sfGFP), streptokinase (SK) and maltose binding protein (MBP), resulting in increased yields compared to previous ELP and BRT17-based methods. Observed yields of purified targets for both systems typically ranged from approximately 200 to 300 micrograms per milliliter of cell culture, while overall recoveries ranged from 10 to 85 percent and were highly dependent on the target protein. Full article
(This article belongs to the Special Issue Polymers for Bioseparations)
Figures

Graphical abstract

Open AccessArticle Extraction of the Polyurethane Layer in Textile Composites for Textronics Applications Using Optical Coherence Tomography
Polymers 2018, 10(5), 469; https://doi.org/10.3390/polym10050469
Received: 28 February 2018 / Revised: 6 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
PDF Full-text (4715 KB) | HTML Full-text | XML Full-text
Abstract
This article presents a new method for the extraction and measurement of the polyurethane layer of Cordura textile composites using optical coherence tomography. The knowledge of coating layer properties in these composites is very important, as it affects mechanical parameters such as stiffness
[...] Read more.
This article presents a new method for the extraction and measurement of the polyurethane layer of Cordura textile composites using optical coherence tomography. The knowledge of coating layer properties in these composites is very important, as it affects mechanical parameters such as stiffness and bending rigidity. Unlike microscopic measurements, which require cross-section samples of the material, the proposed approach is non-invasive. The method is based on detecting the top and bottom boundaries of the polyurethane layer in Optical Coherence Tomography (OCT) images using image processing methods, namely edge enhancement filtering, thresholding and spline smoothing. The cover layer measurement results obtained from a three-dimensional OCT image of the composite fabric are presented as the thickness maps. The average values of the layer thicknesses measured with the OCT method for four types of Cordura showed a high correlation with the results obtained from microscopic measurements (Pearson correlation coefficient r = 0.9844 ), which confirms the accuracy of the OCT method. Full article
Figures

Figure 1

Open AccessArticle A Temperature-Tunable Thiophene Polymer Laser
Polymers 2018, 10(5), 470; https://doi.org/10.3390/polym10050470
Received: 19 March 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
PDF Full-text (4929 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports a temperature-tunable conjugated polymer poly[3-(2-ethyl-isocyanato-octadecanyl)-thiophene] (TCP) laser working in superradiant (SR)—or amplified spontaneous emission (ASE)—mode. The absorption spectra indicated the aggregate (mostly dimer) formation upon increasing concentration and/or decreasing temperature. Amplified spontaneous emission (ASE) was observed at suitable concentration, temperature,
[...] Read more.
This paper reports a temperature-tunable conjugated polymer poly[3-(2-ethyl-isocyanato-octadecanyl)-thiophene] (TCP) laser working in superradiant (SR)—or amplified spontaneous emission (ASE)—mode. The absorption spectra indicated the aggregate (mostly dimer) formation upon increasing concentration and/or decreasing temperature. Amplified spontaneous emission (ASE) was observed at suitable concentration, temperature, and pump energy values. The efficiency of the ASE from the TCP polymer was improved by energy transfer from an oligomer [1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene]. Moreover, the ASE wavelength can be tuned between 550 and 610 nm by changing the temperature of the solution from 60 to 10 °C. To the best of our knowledge, this is the first report of a high-power, temperature-tunable, and conjugated polymer laser. Full article
Figures

Graphical abstract

Open AccessArticle Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, II: An Efficient and Facile Method to Synthesize High Molecular Weight Polyester Appropriate for Food Packaging Applications
Polymers 2018, 10(5), 471; https://doi.org/10.3390/polym10050471
Received: 10 April 2018 / Revised: 20 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
PDF Full-text (25113 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The goal of this study was to synthesize, through a facile strategy, high molecular weight poly(ethylene furanoate) (PEF), which could be applicable in food packaging applications. The efficient method to generate PEF with high molecular weight consists of carrying out a first solid-state
[...] Read more.
The goal of this study was to synthesize, through a facile strategy, high molecular weight poly(ethylene furanoate) (PEF), which could be applicable in food packaging applications. The efficient method to generate PEF with high molecular weight consists of carrying out a first solid-state polycondensation under vacuum for 6 h reaction time at 205 °C for the resulting polymer from two-step melt polycondensation process, which is catalyzed by tetrabutyl titanate (TBT). A remelting step was thereafter applied for 15 min at 250 °C for the obtained polyester. Thus, the PEF sample was ground into powder, and was then crystallized for 6 h at 170 °C. This polyester is then submitted to a second solid-state polycondensation (SSP) carried out at different reaction times (1, 2, 3.5, and 5 h) and temperatures 190, 200, and 205 °C, under vacuum. Ultimately, a significant increase in intrinsic viscosity is observed with only 5 h reaction time at 205 °C during the second SSP being needed to obtain very high molecular weight PEF polymer greater than 1 dL/g, which sufficient for manufacturing purposes. Intrinsic viscosity (IV), carboxyl end-group content (–COOH), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polyesters. Thanks to the post-polymerization process, DSC results showed that the melting temperatures of the prepared PEF samples were steadily enhanced in an obvious way as a function of reaction time and temperature increase. It was revealed, as was expected for all SSP samples, that the intrinsic viscosity and the average molecular weight of PEF polyester increased with increasing SSP time and temperature, whereas the number of carboxyl end-group concentration was decreased. A simple kinetic model was also developed and used to predict the time evolution of polyesters IV, as well as the carboxyl and hydroxyl end-groups of PEF during the SSP. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
Figures

Graphical abstract

Open AccessArticle Modeling of Flexible Polyurethane Foam Shrinkage for Bra Cup Moulding Process Control
Polymers 2018, 10(5), 472; https://doi.org/10.3390/polym10050472
Received: 22 March 2018 / Revised: 20 April 2018 / Accepted: 21 April 2018 / Published: 26 April 2018
PDF Full-text (3162 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, moulding technology has become a remarkable manufacturing process in the intimate apparel industry. Polyurethane (PU) foam sheets are used to mould three-dimensional (3D) seamless bra cups of various softness and shapes, which eliminate bulky seams and reduce production costs. However, it has
[...] Read more.
Nowadays, moulding technology has become a remarkable manufacturing process in the intimate apparel industry. Polyurethane (PU) foam sheets are used to mould three-dimensional (3D) seamless bra cups of various softness and shapes, which eliminate bulky seams and reduce production costs. However, it has been challenging to accurately and effectively control the moulding process and bra cup thickness. In this study, the theoretical mechanism of heat transfer and the thermal conductivity of PU foams are first examined. Experimental studies are carried out to investigate the changes in foam materials at various moulding conditions (viz., temperatures, and lengths of dwell time) in terms of surface morphology and thickness by using electron and optical microscopy. Based on the theoretical and experimental investigations of the thermal conductivity of the foam materials, empirical equations of shrinkage ratio and thermal conduction of foam materials were established. A regression model to predict flexible PU foam shrinkage during the bra cup moulding process was formulated by using the Levenberg-Marquardt method of nonlinear least squares algorithm and verified for accuracy. This study therefore provides an effective approach that optimizes control of the bra cup moulding process and assures the ultimate quality and thickness of moulded foam cups. Full article
(This article belongs to the Special Issue Polymer Processing for Enhancing Textile Application)
Figures

Graphical abstract

Open AccessArticle Effect of Elevated Temperature Annealing on Nafion/SiO2 Composite Membranes for the All-Vanadium Redox Flow Battery
Polymers 2018, 10(5), 473; https://doi.org/10.3390/polym10050473
Received: 12 March 2018 / Revised: 19 April 2018 / Accepted: 20 April 2018 / Published: 26 April 2018
PDF Full-text (3481 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Conducting Nafion/SiO2 composite membranes were successfully prepared using a simple electrostatic self-assembly method, followed by annealing at elevated temperatures of 240, 270, and 300 °C. Membrane performance was then investigated in vanadium redox flow batteries (VRB). These annealed composite membranes demonstrated lower
[...] Read more.
Conducting Nafion/SiO2 composite membranes were successfully prepared using a simple electrostatic self-assembly method, followed by annealing at elevated temperatures of 240, 270, and 300 °C. Membrane performance was then investigated in vanadium redox flow batteries (VRB). These annealed composite membranes demonstrated lower vanadium permeability and a better selectivity coefficient than pure Nafion membranes. The annealing temperature of 270 °C created the highest proton conductivity in the Nafion/SiO2 composite membranes. The microstructures of these membranes were analyzed using transmission electron microscopy, small-angle X-ray scattering, and positron annihilation lifetime spectroscopy. This study revealed that exposure to high temperatures resulted in an increase in the free volumes of the composite membranes, resulting in improved mechanical and chemical behavior, with the single cell system containing composite membranes performing better than systems containing pure Nafion membranes. Full article
(This article belongs to the Special Issue Polymeric Materials for Electrochemical Energy Conversion and Storage)
Figures

Graphical abstract

Open AccessArticle Near-Infrared Light and Solar Light Activated Self-Healing Epoxy Coating having Enhanced Properties Using MXene Flakes as Multifunctional Fillers
Polymers 2018, 10(5), 474; https://doi.org/10.3390/polym10050474
Received: 2 April 2018 / Revised: 19 April 2018 / Accepted: 23 April 2018 / Published: 26 April 2018
PDF Full-text (7887 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Two issues are required to be solved to bring intrinsically self-healing polymer coatings into real applications: remote activation and satisfied practical properties. Here, we used MXene, a newly reported two-dimensional material, to provide an epoxy coating with light-induced self-healing capabilities and we worked
[...] Read more.
Two issues are required to be solved to bring intrinsically self-healing polymer coatings into real applications: remote activation and satisfied practical properties. Here, we used MXene, a newly reported two-dimensional material, to provide an epoxy coating with light-induced self-healing capabilities and we worked to enhance the properties of that coating. The self-healing coatings had a reversible crosslinking network based on the Diels-Alder reaction among maleimide groups from bis(4-maleimidopheny)methane and dangling furan groups in oligomers that were prepared through the condensation polymerization of diglycidylether of bisphenol A and furfurylamine. The results showed that the delaminated MXene flakes were small in size, around 900 nm, and dispersed well in self-healing coatings. The MXene flakes of only 2.80 wt % improved greatly the pencil hardness of the coating hardness from HB to 5H and the polarization resistance from 4.3 to 428.3 MΩ cm−2. The self-healing behavior, however, was retarded by MXene flakes. Leveling agent acted a key part here to facilitate the gap closure driven by reverse plasticity to compensate for the limitation of macromolecular mobility resulting from the MXene flakes. The self-healing of coatings was achieved in 30 s by thermal treatment at 150 °C. The efficient self-healing was also demonstrated based on the recovery of the anti-corrosion capability. MXene flakes also played an evident photothermal role in generating heat via irradiation of near-infrared light at 808 nm and focused sunlight. The healing can be quickly obtained in 10 s under irradiation of near-infrared light at 808 nm having a power density of 6.28 W cm−2 or in 10 min under irradiation of focused sunlight having a power density of 4.0 W cm−2. Full article
(This article belongs to the Special Issue Surface Modification and Functional Coatings for Polymers)
Figures

Graphical abstract

Open AccessArticle Coarse-Grained Simulations of Aqueous Thermoresponsive Polyethers
Polymers 2018, 10(5), 475; https://doi.org/10.3390/polym10050475
Received: 7 February 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 27 April 2018
PDF Full-text (466 KB) | HTML Full-text | XML Full-text
Abstract
Thermoresponsive polymers can change structure or solubility as a function of temperature. Block co-polymers of polyethers have a response that depends on polymer molecular weight and co-polymer composition. A coarse-grained model for aqueous polyethers is developed and applied to polyethylene oxide and polyethylene
[...] Read more.
Thermoresponsive polymers can change structure or solubility as a function of temperature. Block co-polymers of polyethers have a response that depends on polymer molecular weight and co-polymer composition. A coarse-grained model for aqueous polyethers is developed and applied to polyethylene oxide and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock co-polymers. In this model, no interaction sites on hydrogen atoms are included, no Coulombic interactions are present, and all interactions are short-ranged, treated with a combination of two- and three-body terms. Our simulations find that The triblock co-polymers tend to associate at temperatures above 350 K. The aggregation is stabilized by contact between The hydrophobic methyl groups on The propylene oxide monomers and involves a large, favorable change in entropy. Full article
(This article belongs to the Special Issue Stimuli Responsive Polymers)
Figures

Graphical abstract

Open AccessArticle New Insight into Polydopamine@ZIF-8 Nanohybrids: A Zinc-Releasing Container for Potential Anticancer Activity
Polymers 2018, 10(5), 476; https://doi.org/10.3390/polym10050476
Received: 19 March 2018 / Revised: 22 April 2018 / Accepted: 23 April 2018 / Published: 27 April 2018
PDF Full-text (3939 KB) | HTML Full-text | XML Full-text
Abstract
Despite the initial evidence on the role of zinc and zinc transporters in cancer prevention, little attention has been paid to the zinc-derived compounds. In the present work, we reported a strategy to prepare a kind of zinc-releasing container with enhanced biocompatibility and
[...] Read more.
Despite the initial evidence on the role of zinc and zinc transporters in cancer prevention, little attention has been paid to the zinc-derived compounds. In the present work, we reported a strategy to prepare a kind of zinc-releasing container with enhanced biocompatibility and release dynamics using ZIF-8 nanocrystals as the sacrificial templates. Transmission electron microscopy (TEM) analysis demonstrated that the ZIF-8 nanocrystals were gradually etched out in the aqueous media within 48 h, resulting in hollow nanocapsules. Notably, we found the self-polymerization of dopamine can form nanoshells around the ZIF-8 nanocrystals, which served as a type of functional membranes during the release of zinc. More interestingly, PDA@ZIF-8–based nanohybrids expressed stronger inhibition to the cancer cell growth, which implied that the nanohybrids could be a drug carrier for chemotherapy. This study broadens the biomedical application of ZIF-8 and also provides a versatile strategy toward the development of multifunctional delivery system. Full article
(This article belongs to the Special Issue Nanostructured Polymers and Nanocomposites)
Figures

Graphical abstract

Open AccessArticle Effects of Graphene Nanoplatelet Size and Surface Area on the AC Electrical Conductivity and Dielectric Constant of Epoxy Nanocomposites
Polymers 2018, 10(5), 477; https://doi.org/10.3390/polym10050477
Received: 3 April 2018 / Revised: 19 April 2018 / Accepted: 25 April 2018 / Published: 27 April 2018
PDF Full-text (9599 KB) | HTML Full-text | XML Full-text
Abstract
Epoxy nanocomposites reinforced with various grades of multilayer graphene nanoplatelets (GNPs) are manufactured and tested. The effects of size, surface area, and concentration of GNP, as well as alternating current (AC) frequency on the electrical and dielectric properties of epoxy nanocomposites are experimentally
[...] Read more.
Epoxy nanocomposites reinforced with various grades of multilayer graphene nanoplatelets (GNPs) are manufactured and tested. The effects of size, surface area, and concentration of GNP, as well as alternating current (AC) frequency on the electrical and dielectric properties of epoxy nanocomposites are experimentally investigated. GNPs with larger size and surface area are always beneficial to increase the electrical conductivity of the composites. However, their effects on the dielectric constant are highly dependent on GNP concentration and AC frequency. At lower GNP concentration, the dielectric constant increases proportionally with the increase in GNP size, while decreasing as the AC frequency increases. At higher GNP concentration in epoxy, the dielectric constant first increases with the increase of the GNP size, but decreases thereafter. This trend is also observed for varying the processed GNP surface area on the dielectric constant. Moreover, the variations of the electrical conductivity and dielectric constant with the GNP concentration and AC frequency are then correlated with the measured interfiller spacing and GNP diameter. Full article
Figures

Graphical abstract

Open AccessArticle Permeability of Novel Chitosan-g-Poly(Methyl Methacrylate) Amphiphilic Nanoparticles in a Model of Small Intestine In Vitro
Polymers 2018, 10(5), 478; https://doi.org/10.3390/polym10050478
Received: 18 April 2018 / Revised: 22 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
PDF Full-text (4154 KB) | HTML Full-text | XML Full-text
Abstract
Engineering of drug nanocarriers combining fine-tuned mucoadhesive/mucopenetrating properties is currently being investigated to ensure more efficient mucosal drug delivery. Aiming to improve the transmucosal delivery of hydrophobic drugs, we designed a novel nanogel produced by the self-assembly of amphiphilic chitosan graft copolymers ionotropically
[...] Read more.
Engineering of drug nanocarriers combining fine-tuned mucoadhesive/mucopenetrating properties is currently being investigated to ensure more efficient mucosal drug delivery. Aiming to improve the transmucosal delivery of hydrophobic drugs, we designed a novel nanogel produced by the self-assembly of amphiphilic chitosan graft copolymers ionotropically crosslinked with sodium tripolyphosphate. In this work, we synthesized, for the first time, chitosan-g-poly(methyl methacrylate) nanoparticles thiolated by the conjugation of N-acetyl cysteine. First, we confirmed that both non-crosslinked and crosslinked nanoparticles in the 0.05–0.1% w/v concentration range display very good cell compatibility in two cell lines that are relevant to oral delivery, Caco-2 cells that mimic the intestinal epithelium and HT29-MTX cells that are a model of mucin-producing goblet cells. Then, we evaluated the effect of crosslinking, nanoparticle concentration, and thiolation on the permeability in vitro utilizing monolayers of (i) Caco-2 and (ii) Caco-2:HT29-MTX cells (9:1 cell number ratio). Results confirmed that the ability of the nanoparticles to cross Caco-2 monolayer was affected by the crosslinking. In addition, thiolated nanoparticles interact more strongly with mucin, resulting in a decrease of the apparent permeability coefficient (Papp) compared to the pristine nanoparticles. Moreover, for all the nanoparticles, higher concentration resulted in lower Papp, suggesting that the transport pathways can undergo saturation. Full article
(This article belongs to the Special Issue Polymers for Therapy and Diagnostics)
Figures

Graphical abstract

Open AccessArticle Modifying an Active Compound’s Release Kinetic Using a Supercritical Impregnation Process to Incorporate an Active Agent into PLA Electrospun Mats
Polymers 2018, 10(5), 479; https://doi.org/10.3390/polym10050479
Received: 12 April 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
PDF Full-text (2388 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The main objective of this work was to study the release of cinnamaldehyde (CIN) from electrospun poly lactic acid (e-PLA) mats obtained through two techniques: (i) direct incorporation of active compound during the electrospinning process (e-PLA-CIN); and (ii) supercritical
[...] Read more.
The main objective of this work was to study the release of cinnamaldehyde (CIN) from electrospun poly lactic acid (e-PLA) mats obtained through two techniques: (i) direct incorporation of active compound during the electrospinning process (e-PLA-CIN); and (ii) supercritical carbon dioxide (scCO2) impregnation of CIN within electrospun PLA mats (e-PLA/CINimp). The development and characterization of both of these active electrospun mats were investigated with the main purpose of modifying the release kinetic of this active compound. Morphological, structural, and thermal properties of these materials were also studied, and control mats e-PLA and e- PLA CO 2 were developed in order to understand the effect of electrospinning and scCO2 impregnation, respectively, on PLA properties. Both strategies of incorporation of this active compound into PLA matrix resulted in different morphologies that influenced chemical and physical properties of these composites and in different release kinetics of CIN. The electrospinning and scCO2 impregnation processes and the presence of CIN altered PLA thermal and structural properties when compared to an extruded PLA material. The incorporation of CIN through scCO2 impregnation resulted in higher release rate and lower diffusion coefficients when compared to active electrospun mats with CIN incorporated during the electrospinning process. Full article
(This article belongs to the Special Issue Electrospinning of Nanofibres)
Figures

Graphical abstract

Open AccessArticle Preparation of PLGA/MWCNT Composite Nanofibers by Airflow Bubble-Spinning and Their Characterization
Polymers 2018, 10(5), 481; https://doi.org/10.3390/polym10050481
Received: 6 April 2018 / Revised: 24 April 2018 / Accepted: 26 April 2018 / Published: 28 April 2018
PDF Full-text (5694 KB) | HTML Full-text | XML Full-text
Abstract
Poly(lactic-co-glycolic acid) (PLGA)/multi-walled carbon nanotube (MWCNT) composite nanofibers have been successfully fabricated via airflow bubble-spinning. In this work, a systematic study of the effects of solution concentration, relative humidity (RH), and composition on the morphology of PLGA nanofibers is reported. By
[...] Read more.
Poly(lactic-co-glycolic acid) (PLGA)/multi-walled carbon nanotube (MWCNT) composite nanofibers have been successfully fabricated via airflow bubble-spinning. In this work, a systematic study of the effects of solution concentration, relative humidity (RH), and composition on the morphology of PLGA nanofibers is reported. By comparing the distribution of fiber diameter, we found that the spinning effect was the best when the temperature was kept at 25 °C, the collecting distance 18 cm, the concentration 8 wt %, and the relative humidity 65%. MWCNTs used as added nanoparticles were incorporated into the PLGA nanofibers. The volatile solvents were used to achieve the purpose of producing nanoporous fibers. Besides, the rheological properties of solutions were studied and the PLGA or PLGA/MWCNT composite nanofibers with a nanoporous structure were also completely characterized using scanning electron microscope (SEM), a thermogravimetric analyzer(TGA), X-ray diffraction(XRD) and Fourier-transform infrared (FTIR) spectroscopy. In addition, we compared the mechanical properties of the fibers. It was found that the addition of MWCNTs significantly enhanced the tensile strength and elasticity of composite nanofibers without compromising the nanoporous morphology. The results showed that the breaking strength of the composite fiber bundle was three times as strong as the pure one, and the elongation at the break was twice as great. This work provided a novel technique successfully not only to get rid of the potential safety hazards caused by unexpected static but also prepare oriented nanoporous fibers, which would demonstrate an impressive prospect for the fields of adsorption and filtration. Full article
(This article belongs to the Special Issue Electrospinning of Nanofibres)
Figures

Graphical abstract

Open AccessArticle Reconfigurable Shape Memory and Self-Welding Properties of Epoxy Phenolic Novolac/Cashew Nut Shell Liquid Composites Reinforced with Carbon Nanotubes
Polymers 2018, 10(5), 482; https://doi.org/10.3390/polym10050482
Received: 11 March 2018 / Revised: 8 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
PDF Full-text (14192 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Conventional shape memory polymers (SMPs) can memorize their permanent shapes. However, these SMPs cannot reconfigure their original shape to obtain a desirable geometry owing to permanent chemically or physically crosslinked networks. To overcome this limitation, novel SMPs that can be reconfigured via bond
[...] Read more.
Conventional shape memory polymers (SMPs) can memorize their permanent shapes. However, these SMPs cannot reconfigure their original shape to obtain a desirable geometry owing to permanent chemically or physically crosslinked networks. To overcome this limitation, novel SMPs that can be reconfigured via bond exchange reactions (BERs) have been developed. In this study, polymer composites consisting of epoxy phenolic novolac (EPN) and bio-based cashew nut shell liquid (CNSL) reinforced by multi-walled carbon nanotubes (CNTs) were prepared. The obtained composites exhibited shape memory and self-welding properties, and their shapes could be reconfigured via BERs. Their shape memory mechanisms were investigated using variable-temperature Fourier transform infrared spectroscopy and dynamic mechanical analysis. The EPN/CNSL composite containing 0.3 wt % CNTs showed the highest shape fixity and shape recovery ratio. Furthermore, shape memory behavior induced by irradiation of near-infrared (NIR) light was also observed. All samples showed high shape recovery ratios of nearly 100% over five cycles, and increasing the CNT content shortened the recovery time remarkably. The ability of shape reconfiguration and stress relaxation affected the photo-induced shape memory properties of reshaped samples. Additionally, the self-welding properties were also influenced by stress relaxation. The hindrance of stress relaxation caused by the CNTs resulted in a decrease in adhesive fracture energy (Gc). However, the Gc values of EPN/CNSL composites were comparable to those of epoxy vitrimers. These results revealed that the material design concepts of thermal- and photo-induced shape memory, shape reconfiguration, and self-welding were combined in the EPN/CNSL composites, which could be feasible method for advanced smart material applications. Full article
(This article belongs to the Special Issue Smart Polymers)
Figures

Graphical abstract

Open AccessArticle Partially Renewable Poly(butylene 2,5-furandicarboxylate-co-isophthalate) Copolyesters Obtained by ROP
Polymers 2018, 10(5), 483; https://doi.org/10.3390/polym10050483
Received: 5 April 2018 / Revised: 23 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
PDF Full-text (9400 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Cyclic butylene furandicarboxylate (c(BF)n) and butylene isophthalate (c(BI)n) oligomers obtained by high dilution condensation reaction were polymerized in bulk at 200 °C with Sn(Oct)2 catalyst via ring opening polymerization to give homopolyesters and copolyesters
[...] Read more.
Cyclic butylene furandicarboxylate (c(BF)n) and butylene isophthalate (c(BI)n) oligomers obtained by high dilution condensation reaction were polymerized in bulk at 200 °C with Sn(Oct)2 catalyst via ring opening polymerization to give homopolyesters and copolyesters (coPBFxIy) with weight average molar masses in the 60,000–70,000 g·mol−1 range and dispersities between 1.3 and 1.9. The composition of the copolyesters as determined by NMR was practically the same as that of the feed, and they all showed an almost random microstructure. The copolyesters were thermally stable up to 300 °C and crystalline for all compositions, and have Tg in the 40–20 °C range with values decreasing almost linearly with their content in isophthalate units in the copolyester. Both melting temperature and enthalpy of the copolyesters decreased as the content in butylene isophthalate units increased up to a composition 30/70 (BF/BI), at which the triclinic crystal phase made exclusively of butylene furanoate units changed to the crystal structure of PBI. The partial replacement of furanoate by isophthalate units decreased substantially the crystallizability of PBF. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
Figures

Graphical abstract

Open AccessArticle Synthesis, Characterization and Microstructure of New Liquid Poly(methylhydrosiloxanes) Containing Branching Units SiO4/2
Polymers 2018, 10(5), 484; https://doi.org/10.3390/polym10050484
Received: 28 March 2018 / Revised: 25 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
PDF Full-text (2308 KB) | HTML Full-text | XML Full-text
Abstract
Six liquid branched poly(methylhydrosiloxanes) of new random structures (PMHS-Q), containing quadruple branching units SiO4/2 (Q), both MeHSiO (DH) and Me2SiO (D) chain building units (or only mers MeHSiO), and terminal groups Me3SiO0.5 (M) were prepared
[...] Read more.
Six liquid branched poly(methylhydrosiloxanes) of new random structures (PMHS-Q), containing quadruple branching units SiO4/2 (Q), both MeHSiO (DH) and Me2SiO (D) chain building units (or only mers MeHSiO), and terminal groups Me3SiO0.5 (M) were prepared by a hydrolytic polycondensation method of appropriate organic chlorosilanes and tetraethyl ortosilicate (TEOS), in diethyl ether medium at temperature below 0 °C. Volatile low molecular weight siloxanes were removed by a vacuum distillation at 150–155 °C. Yields of PMHS-Q reached from 55–69 wt%. Their dynamic viscosities were measured in the Brookfield HBDV+IIcP cone-plate viscometer and ranged from 10.7–13.1 cP. Molecular weights (MW) of PMHS-Q (Mn = 2440–6310 g/mol, Mw = 5750–10,350 g/mol) and polydispersities of MW (Mw/Mn = 2.0–2.8) were determined by a size exclusion chromatography (SEC). All polymers were characterized by FTIR, 1H- and 29Si-NMR, and an elemental analysis. A microstructure of siloxane chains was proposed on a basis of 29Si-NMR results and compared with literature data. Full article
(This article belongs to the Special Issue Siloxane-Based Polymers)
Figures

Figure 1

Open AccessArticle High Mechanical and Thermal Properties of Epoxy Composites with Liquid Crystalline Polyurethane Modified Graphene
Polymers 2018, 10(5), 485; https://doi.org/10.3390/polym10050485
Received: 26 March 2018 / Revised: 16 April 2018 / Accepted: 26 April 2018 / Published: 1 May 2018
PDF Full-text (6017 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Graphene nanosheets (GNs) often result in incompatibility with the hydrophobic polymer matrix, and the tendency to form aggregates during processing. Herein, liquid crystalline polyurethane modified GNs (GPLP) were obtained by π–π stacking interactions between GNs and perylene bisimide derivatives, and then in-situ polymerization
[...] Read more.
Graphene nanosheets (GNs) often result in incompatibility with the hydrophobic polymer matrix, and the tendency to form aggregates during processing. Herein, liquid crystalline polyurethane modified GNs (GPLP) were obtained by π–π stacking interactions between GNs and perylene bisimide derivatives, and then in-situ polymerization of liquid-crystalline polyurethane. Spectroscopic studies, elemental analysis, and thermal properties confirmed the successful π–π stacking and the integrated structure of GPLP. The good dispersion state of GPLP in the epoxy matrix (EP), and the strong interactions between GPLP and EP, lead to the significant improvement of the thermal and mechanical performance of the GPLP/EP composites. The impact strength, Young’s modulus, tensile strength, and toughness of the GPLP/EP composites with 1.47 wt % GNs reached the highest values of 54.31 kJ/m2, 530.8 MPa, 112.33 MPa and 863 J/m3, which significantly increased by 210%, 57%, 143%, and 122% compared to that of neat epoxy, respectively. As well, the glass transition temperature increased by a notable 33 °C. It is hoped that this work can be used to exploit more efficient methods to overcome the poor adhesion between GNs and polymers. Full article
(This article belongs to the Special Issue Polymer Hybrids and Composites)
Figures

Graphical abstract

Open AccessArticle Processing and Thermal Response of Temperature-Sensitive-Gel(TSG)/Polymer Composites
Polymers 2018, 10(5), 486; https://doi.org/10.3390/polym10050486
Received: 4 April 2018 / Revised: 26 April 2018 / Accepted: 28 April 2018 / Published: 1 May 2018
PDF Full-text (5747 KB) | HTML Full-text | XML Full-text
Abstract
Temperature-sensitive gels (TSGs) are generally used in the fields of medical, robotics, MEMS, and also in daily life. In this paper, we synthesized a novel TSG with good thermal durability and a lower melting temperature below 60 °C. We discussed the physical properties
[...] Read more.
Temperature-sensitive gels (TSGs) are generally used in the fields of medical, robotics, MEMS, and also in daily life. In this paper, we synthesized a novel TSG with good thermal durability and a lower melting temperature below 60 °C. We discussed the physical properties of he TSG and found it provided excellent thermal expansion. Therefore, we proposed the usage of TSG to develop a strategic breathable film with controllable gas permeability. The TSG particles were prepared firstly and then blended with linear low-density polyethylene/calcium carbonate (LLDPE/CaCO3) composite to develop microporous TSG/LLDPE/CaCO3 films. We investigated the morphology, thermal, and mechanical properties of TSG/LLDPE/CaCO3 composite films. The film characterization was conducted by gas permeability testing and demonstration temperature control experiments. The uniformly porous structure and the pore size in the range of 5–40 μm for the TSG/LLDPE/CaCO3 composite films were indicated by SEM micrographs. The demonstration temperature control experiments clearly proved the effect of the controllable gas permeability of the TSG and, more promisingly, the great practical value and application prospects of this strategic effect for the temperature-sensitive breathable film was proved. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
Figures

Figure 1

Open AccessArticle The Effect of Aromatic Diimide Side Groups on the π-Conjugated Polymer Properties
Polymers 2018, 10(5), 487; https://doi.org/10.3390/polym10050487
Received: 27 March 2018 / Revised: 17 April 2018 / Accepted: 28 April 2018 / Published: 1 May 2018
PDF Full-text (2568 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The presented study describes the method for the synthesis and characterization of a new class of conjugated copolymers containing a perylenediimide (PDI) and naphthalene diimide (NDI) side groups. The main conjugated backbone is a donor-acceptor polymer poly[3,6-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] containing thiophene and carbazole
[...] Read more.
The presented study describes the method for the synthesis and characterization of a new class of conjugated copolymers containing a perylenediimide (PDI) and naphthalene diimide (NDI) side groups. The main conjugated backbone is a donor-acceptor polymer poly[3,6-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] containing thiophene and carbazole as donor units and benzothiadiazole as an acceptor unit. The presented compounds were synthesized in a multistep synthesis. The polymerization was carried out by Suzuki or Stille coupling reaction. Redox properties of the studied polymers were tested in different conditions. Electrochemical investigation revealed independent reduction of the main polymer chain and diimide side groups. UV-Vis spectroscopy revealed the overlap of two absorption spectra. The difference between the electron affinity of the polymer main chain and that of the diimides estimated electrochemically is approximately 0.3 eV. Full article
(This article belongs to the Special Issue π-Stacked Polymers)
Figures

Graphical abstract

Open AccessArticle Fructose-Based Acrylic Copolymers by Emulsion Polymerization
Polymers 2018, 10(5), 488; https://doi.org/10.3390/polym10050488
Received: 12 March 2018 / Revised: 26 April 2018 / Accepted: 27 April 2018 / Published: 2 May 2018
PDF Full-text (2725 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The exploration of a renewable resource for the preparation of waterborne copolymers was conducted. Low molar mass sugar resources were selected for their wide availability. A fructose-based monomer (MF) bearing a methacrylate radically polymerizable group was successfully synthesized. The latter was shown to
[...] Read more.
The exploration of a renewable resource for the preparation of waterborne copolymers was conducted. Low molar mass sugar resources were selected for their wide availability. A fructose-based monomer (MF) bearing a methacrylate radically polymerizable group was successfully synthesized. The latter was shown to be able to homopolymerize in emulsion. The high Tg of the resulting polymer (about 115 °C) makes it of particular interest for adhesive and coating applications where hard materials are necessary to ensure valuable properties. As a result, its incorporation in waterborne acrylic containing formulations as an equivalent to petrochemical-based methyl methacrylate was investigated. It was found that the bio-based monomer exhibited similar behavior to that of common methacrylates, as shown by polymerization kinetics and particle size evolution. Furthermore, the homogeneous incorporation of the sugar units into the acrylate chains was confirmed by a unique glass transition temperature in differential scanning calorimeter (DSC). The potential of MF for the production of waterborne copolymers was greatly valued by the successful increase of formulation solids content up to 45 wt %. Interestingly, polymer insolubility in tetrahydrofurane increased with time due to further reactions occurring in storage. Most likely, the partial deprotection of sugar units was the reason for the creation of hydrogen bonding and, thus, physically insoluble entangled chains. This behavior highlights opportunities to make use of hydroxyl groups either for further functionalization or, eventually, for achieving enhanced adhesion on casted substrates. Full article
(This article belongs to the Special Issue Emulsion Polymerization)
Figures

Graphical abstract

Open AccessArticle A Novel Delivery System for the Controlled Release~of Antimicrobial Peptides: Citropin 1.1 and Temporin A
Polymers 2018, 10(5), 489; https://doi.org/10.3390/polym10050489
Received: 16 April 2018 / Revised: 27 April 2018 / Accepted: 30 April 2018 / Published: 2 May 2018
PDF Full-text (1894 KB) | HTML Full-text | XML Full-text
Abstract
Antimicrobial peptides (AMPs) are prospective therapeutic options for treating multiple-strain infections. However, clinical and commercial development of AMPs has some limitations due to their limited stability, low bioavailability, and potential hemotoxicity. The purpose of this study was to develop new polymeric carriers as
[...] Read more.
Antimicrobial peptides (AMPs) are prospective therapeutic options for treating multiple-strain infections. However, clinical and commercial development of AMPs has some limitations due to their limited stability, low bioavailability, and potential hemotoxicity. The purpose of this study was to develop new polymeric carriers as highly controlled release devices for amphibian peptides citropin 1.1 (CIT) and temporin A (TEMP). The release rate of the active pharmaceutical ingredients (APIs) was strongly dependent on the API characteristics and the matrix microstructure. In the current work, we investigated the effect of the polymer microstructure on in vitro release kinetics of AMPs. Non-contact laser profilometry, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were used to determine the structural changes during matrix degradation. Moreover, geno- and cytotoxicity of the synthesized new carriers were evaluated. The in vitro release study of AMPs from the obtained non-toxic matrices shows that peptides were released with near-zero-order kinetics. The peptide “burst release” effect was not observed. New devices have reached the therapeutic concentration of AMPs within 24 h and maintained it for 28 days. Hence, our results suggest that these polymeric devices could be potentially used as therapeutic options for the treatment of local infections. Full article
(This article belongs to the Special Issue Biocompatible Polymers)
Figures

Graphical abstract

Open AccessArticle Optimisation of the Adhesion of Polypropylene-Based Materials during Extrusion-Based Additive Manufacturing
Polymers 2018, 10(5), 490; https://doi.org/10.3390/polym10050490
Received: 4 April 2018 / Revised: 24 April 2018 / Accepted: 27 April 2018 / Published: 2 May 2018
PDF Full-text (5385 KB) | HTML Full-text | XML Full-text
Abstract
Polypropylene (PP) parts produced by means of extrusion-based additive manufacturing, also known as fused filament fabrication, are prone to detaching from the build platform due to their strong tendency to shrink and warp. Apart from incorporating high volume fractions of fillers, one approach
[...] Read more.
Polypropylene (PP) parts produced by means of extrusion-based additive manufacturing, also known as fused filament fabrication, are prone to detaching from the build platform due to their strong tendency to shrink and warp. Apart from incorporating high volume fractions of fillers, one approach to mitigate this issue is to improve the adhesion between the first deposited layer and the build platform. However, a major challenge for PP is the lack of adhesion on standard platform materials, as well as a high risk of welding on PP-based platform materials. This study reports the material selection of build platform alternatives based on contact angle measurements. The adhesion forces, investigated by shear-off measurements, between PP-based filaments and the most promising platform material, an ultra-high-molecular-weight polyethylene (UHMW-PE), were optimised by a thorough parametric study. Higher adhesion forces were measured by increasing the platform and extrusion temperatures, increasing the flow rate and decreasing the thickness of the first layer. Apart from changes in printer settings, an increased surface roughness of the UHMW-PE platform led to a sufficient, weld-free adhesion for large-area parts of PP-based filaments, due to improved wetting, mechanical interlockings, and an increased surface area between the two materials in contact. Full article
Figures

Graphical abstract

Open AccessArticle Thermal Degradation Kinetics and Viscoelastic Behavior of Poly(Methyl Methacrylate)/Organomodified Montmorillonite Nanocomposites Prepared via In Situ Bulk Radical Polymerization
Polymers 2018, 10(5), 491; https://doi.org/10.3390/polym10050491
Received: 4 April 2018 / Revised: 20 April 2018 / Accepted: 1 May 2018 / Published: 3 May 2018
PDF Full-text (3108 KB) | HTML Full-text | XML Full-text
Abstract
Nanocomposites of polymers with nanoclays have recently found great research interest due to their enhanced thermal and mechanical properties. Deep understanding of the kinetics of thermal degradation of such materials is very important, since the degradation mechanism usually changes in the presence of
[...] Read more.
Nanocomposites of polymers with nanoclays have recently found great research interest due to their enhanced thermal and mechanical properties. Deep understanding of the kinetics of thermal degradation of such materials is very important, since the degradation mechanism usually changes in the presence of the nano-filler. In this investigation, poly(methyl methacrylate)/organomodified clay nanocomposite materials were prepared by the in situ free radical bulk polymerization technique. The thermal degradation of the products obtained was studied by means of thermogravimetric analysis at several heating rates. Isoconversional kinetic analysis was conducted in order to investigate the effect of degradation conversion on the activation energy. Both, pure poly(methyl methacrylate) (PMMA) and its nanocomposites were found to degrade through a two-step reaction mechanism. Data arising from a differential and an integral method were used to disclose the correlation between activation energies (Eα) and the extent of degradation (α). It was found that Eα value improved for all nanocomposites at α values higher than 0.3. Moreover, the viscoelastic behavior of the obtained nanocomposites was examined by means of dynamic mechanical thermal analysis. All nanocomposites exhibited higher storage modulus in comparison to the virgin PMMA at room temperature, while the increment of clay amount improved their stiffness gradually. Full article
(This article belongs to the Special Issue Polymer-Clay (Nano)Composites)
Figures

Graphical abstract

Open AccessArticle Lipid-Lowering Effect of the Pleurotus eryngii (King Oyster Mushroom) Polysaccharide from Solid-State Fermentation on Both Macrophage-Derived Foam Cells and Zebrafish Models
Polymers 2018, 10(5), 492; https://doi.org/10.3390/polym10050492
Received: 1 April 2018 / Revised: 26 April 2018 / Accepted: 27 April 2018 / Published: 3 May 2018
PDF Full-text (2547 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Hyperlipidemia is a key risk factor in inducing fatty liver, hypertension, atherosclerosis and cerebrovascular diseases. Previous studies have verified that polysaccharides from fruiting bodies (PEPE) of Pleurotus eryngii (king oyster mushroom) are capable of decreasing the lipid content. In this study, the P.
[...] Read more.
Hyperlipidemia is a key risk factor in inducing fatty liver, hypertension, atherosclerosis and cerebrovascular diseases. Previous studies have verified that polysaccharides from fruiting bodies (PEPE) of Pleurotus eryngii (king oyster mushroom) are capable of decreasing the lipid content. In this study, the P. eryngii polysaccharide is obtained by solid-state fermentation (PESF) using lignocellulosic wastes, corn-cobs and wheat bran. The high-performance liquid chromatography (HPLC) assays indicate that PESF has a similar composition to that of PEPE. Meanwhile, PESF has no detectable toxicity and is able to significantly inhibit foam-cell formation in murine macrophage cells (RAW264.7) induced by oxidized low-density lipoprotein. Further verification indicates that PESF has lipid-lowering effects during the lipid absorption phase in a zebrafish hyperlipidemia model. Our findings suggest that the P. eryngii polysaccharide from solid-state fermentation (PESF) can be used as a valuable lipid-lowering food additive or raw materials for producing lipid-lowering drugs. Full article
(This article belongs to the Special Issue Polysaccharides)
Figures

Graphical abstract

Open AccessArticle Controlled Levofloxacin Release and Antibacterial Properties of β-Cyclodextrins-Grafted Polypropylene Mesh Devices for Hernia Repair
Polymers 2018, 10(5), 493; https://doi.org/10.3390/polym10050493
Received: 31 March 2018 / Revised: 29 April 2018 / Accepted: 1 May 2018 / Published: 3 May 2018
PDF Full-text (2365 KB) | HTML Full-text | XML Full-text
Abstract
Mesh infection is a major complication of hernia repair. After knitted mesh implantation, bacteria can grow within textile structures causing infection. In this work, polypropylene (PP) mesh devices were two-step grafted with hexamethylene diisocyanate (HDI) and β–cyclodexrins (CD) and then loaded with suitable
[...] Read more.
Mesh infection is a major complication of hernia repair. After knitted mesh implantation, bacteria can grow within textile structures causing infection. In this work, polypropylene (PP) mesh devices were two-step grafted with hexamethylene diisocyanate (HDI) and β–cyclodexrins (CD) and then loaded with suitable antimicrobial levofloxacin HCL for hernia mesh-infection prevention. First, oxygen plasma was able to create surface roughness, then HDI was successfully grafted onto PP fiber surfaces. Afterwards, CD was covalently grafted onto the HDI treated PP meshes, and levofloxacin HCL (LVFX) was loaded into the CD cavity of the modified meshes. The modified devices were evaluated for sustained antibiotic properties and drug-release profiles in a phosphate buffer, and sustained drug release was observed between interfaces of meshes and aqueous environment. The antibiotic-loaded PP mesh samples demonstrated sustained antibacterial properties for 7 and 10 days, respectively, against both Gram-negative and Gram-positive bacteria. The CD-captured levofloxacin HCL showed burst release after 6 h but later exhibited sustained release for the next 48 h. Among all samples, the modified mesh LVFX-6 was more stable and showed more sustained drug release and could be employed in future clinical applications. Full article
(This article belongs to the Special Issue Antimicrobial Polymers)
Figures

Graphical abstract

Open AccessArticle Transformation of H-Aggregates and J-Dimers of Water-Soluble Tetrakis (4-carboxyphenyl) Porphyrin in Polyion Complex Micelles
Polymers 2018, 10(5), 494; https://doi.org/10.3390/polym10050494
Received: 4 April 2018 / Revised: 20 April 2018 / Accepted: 28 April 2018 / Published: 3 May 2018
PDF Full-text (4254 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Tetrakis (4-carboxyphenyl) porphyrin (TCPP) and polyelectrolyte poly(N-methyl-2-vinylpyridinium iodide)-b-poly(ethylene oxide) (PMVP41-b-PEO205) can self-aggregate into polyion complex (PIC) micelles in alkaline aqueous solution. UV-vis spectroscopy, fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering were
[...] Read more.
Tetrakis (4-carboxyphenyl) porphyrin (TCPP) and polyelectrolyte poly(N-methyl-2-vinylpyridinium iodide)-b-poly(ethylene oxide) (PMVP41-b-PEO205) can self-aggregate into polyion complex (PIC) micelles in alkaline aqueous solution. UV-vis spectroscopy, fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering were carried out to study PIC micelles. Density functional theory (DFT) calculation method was applied to study the interaction of TCPP and PMVP41-b-PEO205. We found that the H-aggregates and J-dimers of anionic TCPP transformed in PIC micelles. H-aggregates of TCPP formed at the charge ratio of TCPP/PMVP41-b-PEO205 1:2 and J-dimer species at the charge ratio above 1:4, respectively. It is worth noting that the transformation from H-aggregates to J-dimer species of TCPP occurred just by adjusting the ratio of polymer and TCPP rather than by changing other factors such as pH, temperature, and ions. Full article
(This article belongs to the Special Issue Polymer Hybrids and Composites)
Figures

Graphical abstract

Open AccessArticle Growing ZnO Nanoparticles on Polydopamine-Templated Cotton Fabrics for Durable Antimicrobial Activity and UV Protection
Polymers 2018, 10(5), 495; https://doi.org/10.3390/polym10050495
Received: 12 April 2018 / Revised: 1 May 2018 / Accepted: 2 May 2018 / Published: 3 May 2018
PDF Full-text (3615 KB) | HTML Full-text | XML Full-text
Abstract
This work aims to develop durable functional cotton fabrics by growing zinc oxide (ZnO) nanoparticles on polydopamine (PDA) templates. ZnO nanoparticles were grown on the PDA-templated cotton fabrics by the hydrothermal method at room temperature. The surface morphology, chemical composition, and crystalline structure
[...] Read more.
This work aims to develop durable functional cotton fabrics by growing zinc oxide (ZnO) nanoparticles on polydopamine (PDA) templates. ZnO nanoparticles were grown on the PDA-templated cotton fabrics by the hydrothermal method at room temperature. The surface morphology, chemical composition, and crystalline structure of the ZnO-coated cotton fabrics were characterized by scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The ZnO nanoparticles were found to disperse evenly on the surface of cotton fabrics. The ultraviolet (UV) protection factor (UPF) value of the ZnO-coated cotton fabrics was maintained at 122.5, and 99% reduction in bacterial load was observed against Gluconobacter cerinus even after five cycles of laundering. The PDA was found to be effective in fixing the ZnO seeds tightly on the surface of cotton fabrics, resulting in excellent durability of the coating of ZnO nanoparticles. Full article
(This article belongs to the Special Issue Textile and Textile-Based Materials)
Figures

Graphical abstract

Open AccessArticle Hyperbranched Polysiloxanes Based on Polyhedral Oligomeric Silsesquioxane Cages with Ultra-High Molecular Weight and Structural Tuneability
Polymers 2018, 10(5), 496; https://doi.org/10.3390/polym10050496
Received: 14 March 2018 / Revised: 9 April 2018 / Accepted: 9 April 2018 / Published: 4 May 2018
PDF Full-text (11213 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain
[...] Read more.
Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain energy of isolated small molecule in which all eight silane groups close into rings on the sides of a single cubic cage. The structural tuneability was further demonstrated by use of methyl(3-chloropropyl)diethoxysilane, which generates a polymer with similar ultra-high molecular weight. Introduction of phosphonate groups through the chloropropyl sites later leads to functionalized polymers which can encapsulate various transition metal nanoparticles. Full article
(This article belongs to the Special Issue Siloxane-Based Polymers)
Figures

Graphical abstract

Open AccessArticle Optical Waveguide Tunable Phase Delay Lines Based on the Superior Thermo-Optic Effect of Polymer
Polymers 2018, 10(5), 497; https://doi.org/10.3390/polym10050497
Received: 29 March 2018 / Revised: 30 April 2018 / Accepted: 3 May 2018 / Published: 4 May 2018
PDF Full-text (3944 KB) | HTML Full-text | XML Full-text
Abstract
Strong thermo-optic effect of polymers is useful for fabricating tunable phase-delay devices with low power consumption and wide tuning range. However, if the temperature change is increased to extend the tuning range, an attenuation of the guided light is accompanied by the refractive
[...] Read more.
Strong thermo-optic effect of polymers is useful for fabricating tunable phase-delay devices with low power consumption and wide tuning range. However, if the temperature change is increased to extend the tuning range, an attenuation of the guided light is accompanied by the refractive index gradient across the waveguide core. For three different waveguide structures, in this study, the optimal structure of the device for a variable phase delay line was found by investigating the attenuation and interference phenomena accompanying phase modulation. By improving the uniformity of thermal distribution across the waveguide core, a phase delay of 130π rad was obtained with an output attenuation less than 0.5 dB. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
Figures

Figure 1

Open AccessArticle Effects of Fatty Acid Anhydride on the Structure and Thermal Properties of Cellulose-g-Polyoxyethylene (2) Hexadecyl Ether
Polymers 2018, 10(5), 498; https://doi.org/10.3390/polym10050498
Received: 23 March 2018 / Revised: 14 April 2018 / Accepted: 20 April 2018 / Published: 4 May 2018
PDF Full-text (4048 KB) | HTML Full-text | XML Full-text
Abstract
Cellulose was premodified by short-chain fatty acid anhydrides, such as acetic anhydride (CA), propionic anhydride (CP), and butyric anhydride (CB), followed by grafting of polyoxyethylene (2) hexadecyl ether (E2C16) using toluene-2,4-diisocyanate as a coupling agent. The feeding molar ratio
[...] Read more.
Cellulose was premodified by short-chain fatty acid anhydrides, such as acetic anhydride (CA), propionic anhydride (CP), and butyric anhydride (CB), followed by grafting of polyoxyethylene (2) hexadecyl ether (E2C16) using toluene-2,4-diisocyanate as a coupling agent. The feeding molar ratio of E2C16 and the anhydroglucose unit (AGU) was fixed at 4:1, and then a series of CA-g-E2C16, CP-g-E2C16, and CB-g-E2C16 copolymers were successfully prepared. The structures and properties of the copolymers were characterized using FTIR (fourier transform infrared spectra), 1H-NMR (Proton nuclear magnetic resonance), DSC (Differential scanning calorimeter), POM (polarized light microscopy), TGA (thermogravimetric analysis) and WAXD (wide-angle X-ray diffraction). It was shown that with the anhydride/AGU ratio increasing, the degree of substitution (DS) value of E2C16 showed a trend of up first and then down. With the carbon chain length increasing, the DS value of E2C16 continuously increases. The phase transition temperature and thermal enthalpy of the copolymers increased with an increasing DS value of E2C16. When the ratio of CB/AGU was 1.5:1, the DS of E2C16 was up to the maximum value of 1.02, and the corresponding melting enthalpy and crystallization enthalpy were 32 J/g and 30 J/g, respectively. The copolymers showed solid–solid phase change behavior. The heat resistant temperature of cellulose-based solid–solid phase change materials was always higher than 270 °C. After the grafting reaction, the crystallinity of E2C16 decreased, while the crystal type was still hexagonal. Full article
Figures

Graphical abstract

Open AccessArticle Tensile Behavior of Polyurethane Organic Polymer and Polypropylene Fiber-Reinforced Sand
Polymers 2018, 10(5), 499; https://doi.org/10.3390/polym10050499
Received: 3 April 2018 / Revised: 30 April 2018 / Accepted: 2 May 2018 / Published: 4 May 2018
PDF Full-text (6744 KB) | HTML Full-text | XML Full-text
Abstract
Physical and chemical reinforcements are commonly used to improve sand properties for engineering requirements. Many researchers have concluded that composite reinforcement can greatly improve sand property strength. In this paper, polyurethane organic polymer (PU) and polypropylene fiber (PF) were used to reinforce sand.
[...] Read more.
Physical and chemical reinforcements are commonly used to improve sand properties for engineering requirements. Many researchers have concluded that composite reinforcement can greatly improve sand property strength. In this paper, polyurethane organic polymer (PU) and polypropylene fiber (PF) were used to reinforce sand. It is found that composite reinforcement has great effects on tensile strength. A series of direct tensile tests were conducted to demonstrate this reinforcement and to investigate the effects of PF content, PU content, dry density, and curing time. Additionally, the reinforcement mechanism was analyzed by scanning electron microscope images. The tensile strength increases with curing time until it reaches a plateau. The composite reinforcement improves the tensile strength exponentially with the increase of PF and PU contents. For the effect due to dry density, the tensile strength first increased and then decreased with the peak at approximately 1.55 g/cm3. Through the interaction force among fibers and sand particles and the bonding force of polymer among sand particles, tensile strength of reinforced sand is greatly improved. Full article
Figures

Graphical abstract

Open AccessArticle Surface Layer Fluorination-Modulated Space Charge Behaviors in HVDC Cable Accessory
Polymers 2018, 10(5), 500; https://doi.org/10.3390/polym10050500
Received: 2 April 2018 / Revised: 28 April 2018 / Accepted: 30 April 2018 / Published: 4 May 2018
PDF Full-text (2009 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Space charges tend to accumulate on the surface and at the interface of ethylene–propylene–diene terpolymer (EPDM), serving as high voltage direct current (HVDC) cable accessory insulation, which likely induces electrical field distortion and dielectric breakdown. Direct fluorination is an effective method to modify
[...] Read more.
Space charges tend to accumulate on the surface and at the interface of ethylene–propylene–diene terpolymer (EPDM), serving as high voltage direct current (HVDC) cable accessory insulation, which likely induces electrical field distortion and dielectric breakdown. Direct fluorination is an effective method to modify the surface characteristics of the EPDM without altering the bulk properties too much. In this paper, the surface morphology, hydrophobic properties, relative permittivity, and DC conductivity of the EPDM before and after fluorination treatment were tested. Furthermore, the surface and interface charge behaviors in the HVDC cable accessory were investigated by the pulsed electroacoustic (PEA) method, and explained from the point of view of trap distribution. The results show that fluorination helps the EPDM polymer obtain lower surface energy and relative permittivity, which is beneficial to the interface match in composite insulation systems. The lowest degree of space charge accumulation occurs in EPDM with 30 min of fluorination. After analyzing the results of the 3D potentials and the density of states (DOS) behaviors in EPDM before and after fluorination, it can be found that fluorination treatment introduces shallower electron traps, and the special electrostatic potential after fluorination can significantly suppress the space charge accumulation at the interface in the HVDC cable accessory. Full article
(This article belongs to the Special Issue Fluorinated Polymers)
Figures

Figure 1

Open AccessArticle Sustainable Boron Nitride Nanosheet-Reinforced Cellulose Nanofiber Composite Film with Oxygen Barrier without the Cost of Color and Cytotoxicity
Polymers 2018, 10(5), 501; https://doi.org/10.3390/polym10050501
Received: 29 March 2018 / Revised: 15 April 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
PDF Full-text (3270 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper introduces a boron nitride nanosheet (BNNS)-reinforced cellulose nanofiber (CNF) film as a sustainable oxygen barrier film that can potentially be applied in food packaging. Most commodity plastics are oxygen-permeable. CNF exhibits an ideal oxygen transmission rate (OTR) of <1 cc/m2
[...] Read more.
This paper introduces a boron nitride nanosheet (BNNS)-reinforced cellulose nanofiber (CNF) film as a sustainable oxygen barrier film that can potentially be applied in food packaging. Most commodity plastics are oxygen-permeable. CNF exhibits an ideal oxygen transmission rate (OTR) of <1 cc/m2/day in highly controlled conditions. A CNF film typically fabricated by the air drying of a CNF aqueous solution reveals an OTR of 19.08 cc/m2/day. The addition of 0–5 wt % BNNS to the CNF dispersion before drying results in a composite film with highly improved OTR of 4.7 cc/m2/day, which is sufficient for meat and cheese packaging. BNNS as a 2D nanomaterial increases the pathway of oxygen gas and reduces the chances of pinhole formation during film fabrication involving water drying. In addition, BNNS improves the mechanical properties of the CNF films (Young’s modulus and tensile strength) without significant elongation reductions, probably due to the good miscibility of CNF and BNNS in the aqueous solution. Addition of BNNS also produces negligible color change, which is important for film aesthetics. An in vitro cell experiment was performed to reveal the low cytotoxicity of the CNF/BNNS composite. This composite film has great potential as a sustainable high-performance food-packaging material. Full article
(This article belongs to the Special Issue Recent Advances in Bioplastics)
Figures

Graphical abstract

Open AccessArticle Barrier Properties of Poly(Propylene Cyclohexanedicarboxylate) Random Eco-Friendly Copolyesters
Polymers 2018, 10(5), 502; https://doi.org/10.3390/polym10050502
Received: 12 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
PDF Full-text (2658 KB) | HTML Full-text | XML Full-text
Abstract
Random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) containing different amounts of neopentyl glycol sub-unit were investigated from the gas barrier point of view at the standard temperature of analysis (23 °C) with respect to the three main gases used in food packaging field: N2
[...] Read more.
Random copolymers of poly(propylene 1,4-cyclohexanedicarboxylate) containing different amounts of neopentyl glycol sub-unit were investigated from the gas barrier point of view at the standard temperature of analysis (23 °C) with respect to the three main gases used in food packaging field: N2, O2, and CO2. The effect of temperature was also evaluated, considering two temperatures close to the Tg sample (8 and 15 °C) and two above Tg (30 and 38 °C). Barrier performances were checked after food contact simulants and in different relative humidity (RH) environments obtained with two saturated saline solutions (Standard Atmosphere, 23 °C, 85% of RH, with saturated KCl solution; Tropical Climate, 38 °C, 90% RH, with saturated KNO3 solution). The results obtained were compared to those of untreated film, which was used as a reference. The relationships between the gas transmission rate, the diffusion coefficients, the solubility, and the copolymer composition were established. The results highlighted a correlation between barrier performance and copolymer composition and the applied treatment. In particular, copolymerization did not cause a worsening of the barrier properties, whereas the different treatments differently influenced the gas barrier behavior, depending on the chemical polymer structure. After treatment, Fourier transform infrared analysis confirmed the chemical stability of these copolymers. Films were transparent, with a light yellowish color, slightly more intense after all treatments. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
Figures

Graphical abstract

Open AccessArticle Grafting Polytetrafluoroethylene Micropowder via in Situ Electron Beam Irradiation-Induced Polymerization
Polymers 2018, 10(5), 503; https://doi.org/10.3390/polym10050503
Received: 11 April 2018 / Revised: 28 April 2018 / Accepted: 4 May 2018 / Published: 6 May 2018
PDF Full-text (5094 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Decreasing the surface energy of polyacrylate-based materials is important especially in embossed holography, but current solutions typically involve high-cost synthesis or encounter compatibility problems. Herein, we utilize the grafting of polytetrafluoroethylene (PTFE) micropowder with poly (methyl methacrylate) (PMMA). The grafting reaction is implemented
[...] Read more.
Decreasing the surface energy of polyacrylate-based materials is important especially in embossed holography, but current solutions typically involve high-cost synthesis or encounter compatibility problems. Herein, we utilize the grafting of polytetrafluoroethylene (PTFE) micropowder with poly (methyl methacrylate) (PMMA). The grafting reaction is implemented via in situ electron beam irradiation-induced polymerization in the presence of fluorinated surfactants, generating PMMA grafted PTFE micropowder (PMMA–g–PTFE). The optimal degree of grafting (DG) is 17.8%. With the incorporation of PMMA–g–PTFE, the interfacial interaction between polyacrylate and PTFE is greatly improved, giving rise to uniform polyacrylate/PMMA–g–PTFE composites with a low surface energy. For instance, the loading content of PMMA–g–PTFE in polyacrylate is up to 16 wt %, leading to an increase of more than 20 degrees in the water contact angle compared to the pristine sample. This research paves a way to generate new polyacrylate-based films for embossed holography. Full article
Figures

Graphical abstract

Open AccessArticle One-Pot Synthesis and Characterization of Novel Shape-Memory Poly(ε-Caprolactone) Based Polyurethane-Epoxy Co-networks with Diels–Alder Couplings
Polymers 2018, 10(5), 504; https://doi.org/10.3390/polym10050504
Received: 7 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 6 May 2018
PDF Full-text (4943 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The present work aimed at the preparation and investigation of different epoxy-polyurethane (EP-PU) co-networks. The EP-PU co-networks were obtained by applying two different synthetic strategies, in which the coupling element, the Diels–Alder (DA) adduct, was prepared previously or formed “in situ” in the
[...] Read more.
The present work aimed at the preparation and investigation of different epoxy-polyurethane (EP-PU) co-networks. The EP-PU co-networks were obtained by applying two different synthetic strategies, in which the coupling element, the Diels–Alder (DA) adduct, was prepared previously or formed “in situ” in the reaction between furan functionalized polyurethane and furfuryl amine-diglycidyl ether bisphenol-A oligomers (FA_DGEBA). For the synthesis of these EP-PU networks, poly(ε-caprolactone)-diol (PCD, Mn = 2 kg/mol) and poly(ε-caprolactone) (PCL) with different molecular weights (Mn = 10, 25 and 50 kg/mol) and 1,6-hexamethylenediisocyanate (HDI) were used. The EP-PU co-networks were characterized by Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (AT-FT-IR), differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). Scanning electron microscopy (SEM) was applied to assess the morphology of the EP-PU samples. It was demonstrated that the stress–strain curves for the EP-PUs could be interpreted based on the Standard Linear Solid (SLS) model. The DMA traces of some EP-PUs (depending on the composition and the synthetic method) revealed a plateau-like region above the melting temperature (Tm) of PCL confirming the presence of cross-linked structure. This feature predicted shape memory (SM) behavior for these EP-PU samples. Indeed, very good shape fixity and moderate shape recovery were obtained. The shape recovery processes of these EP-PU samples were described using double exponential decay functions. Full article
(This article belongs to the Special Issue Smart and Modern Thermoplastic Polymer Materials)
Figures

Figure 1

Open AccessArticle Solid-State Nuclear Magnetic Resonance (NMR) and Nuclear Magnetic Relaxation Time Analyses of Molecular Mobility and Compatibility of Plasticized Polyhydroxyalkanoates (PHA) Copolymers
Polymers 2018, 10(5), 506; https://doi.org/10.3390/polym10050506
Received: 19 April 2018 / Revised: 3 May 2018 / Accepted: 5 May 2018 / Published: 7 May 2018
PDF Full-text (3719 KB) | HTML Full-text | XML Full-text
Abstract
The molecular mobility and compatibility of plasticized polyhydroxyalkanoates (PHA) were investigated, focusing on changes due to copolymerization using either flexible poly (butylene succinate) (PBS) or rigid poly(lactic acid) (PLA) units. For the case of a poly(3-hydroxybutyrate) (PHB) unit in plasticized PHA, copolymerization of
[...] Read more.
The molecular mobility and compatibility of plasticized polyhydroxyalkanoates (PHA) were investigated, focusing on changes due to copolymerization using either flexible poly (butylene succinate) (PBS) or rigid poly(lactic acid) (PLA) units. For the case of a poly(3-hydroxybutyrate) (PHB) unit in plasticized PHA, copolymerization of either PBS or PLA decreased 1H and 13C spin-lattice relaxation times in the laboratory frame (T1H and T1C) in the same manner, while PBS produced a lower 1H spin-lattice relaxation time in the rotating frame (T1ρH) than PLA. Both the signals of 1H MAS (magic-angle spinning) and 13C PST (pulse saturation transfer) MAS nuclear magnetic resonance (NMR) spectra were sharpened and increased by copolymerization with PBS. A variable temperature relaxation time analysis showed that the decrease of T1H values was dominated by the 1H spin diffusion via the interface between PHB and the added polyester because of the good compatibility. Meanwhile, the decrease of T1C values was dominated by increasingly rapid molecular motions of PHB because of the lowered crystallinity due to the plasticization. Slow molecular motions (kHz order) were enhanced more by the addition of PBS than PLA, although rapid molecular motions (MHz order) were enhanced by either polyester. Several NMR parameters were beneficial for analyzing the manufacturing process as the indexes of polymer compatibility and molecular motions. Full article
(This article belongs to the Special Issue NMR in Polymer Science)
Figures

Graphical abstract

Open AccessArticle Controlled Preparation of Thermally Stable Fe-Poly(dimethylsiloxane) Composite by Magnetic Induction Heating
Polymers 2018, 10(5), 507; https://doi.org/10.3390/polym10050507
Received: 1 April 2018 / Revised: 24 April 2018 / Accepted: 4 May 2018 / Published: 7 May 2018
PDF Full-text (1775 KB) | HTML Full-text | XML Full-text
Abstract
The most challenging task in the preparation of poly(dimethylsiloxane) composites is to control the curing time as well as to enhance their thermal and swelling behavior. Curing rate can be modified and controlled by a range of iron powder contents to achieve a
[...] Read more.
The most challenging task in the preparation of poly(dimethylsiloxane) composites is to control the curing time as well as to enhance their thermal and swelling behavior. Curing rate can be modified and controlled by a range of iron powder contents to achieve a desired working time, where iron is used as self-heating particles. Iron under alternative current magnetic field (ACMF) is able to generate thermal energy, providing a benefit in accelerating the curing of composites. Three types of iron-Poly(dimethylsiloxane) (Fe-PDMS) composites were prepared under ACMF with iron content 5, 10, and 15 wt %. The curing process was investigated by FTIR, while the morphology and the thermal stability were examined by SEM, DMA, and TGA. The heating’s profile was studied as functions of iron content and induction time. It was found that the time required to complete curing was reduced and the curing temperature was controlled by varying the iron content and induction time. In addition, the thermal stability and the swelling behavior of the prepared composites were enhanced in comparison with the conventional PDMS and thus offer a promising route to obtain thermally stable composites. Full article
(This article belongs to the Special Issue Magnetic Field in Polymer Research)
Figures

Graphical abstract

Open AccessArticle The Coordination and Luminescence of the Eu(III) Complexes with the Polymers (PMMA, PVP)
Polymers 2018, 10(5), 508; https://doi.org/10.3390/polym10050508
Received: 21 March 2018 / Revised: 21 April 2018 / Accepted: 4 May 2018 / Published: 7 May 2018
PDF Full-text (7699 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The rare earth complexes and the polymers can be made into composite nanofibers through electrospinning. The fluorescence intensity of these fiber composites is much higher than that of the rare earth complexes. By changing the mixed proportion of polymethyl methacrylate (PMMA) and complexes,
[...] Read more.
The rare earth complexes and the polymers can be made into composite nanofibers through electrospinning. The fluorescence intensity of these fiber composites is much higher than that of the rare earth complexes. By changing the mixed proportion of polymethyl methacrylate (PMMA) and complexes, nanofiber materials were prepared. Then, by measuring their fluorescence intensity, it is found that the carbonyl bond of PMMA may have coordinated with the rare earth ions and enhanced the luminescence intensity of them. Then, a series of experiments were designed to study their coordination and luminescence mechanism. The coordination mechanism of the polymers with carbonyl groups and the rare earth complexes was explained by Eu(TFT)3(TPPO), Eu(TFT)3(TPPO)2, Eu(PFP)3(TPPO), Eu(PFP)3(TPPO)2, and polyvinyl pyrrolidone (PVP) dissolved in chloroform solution, where TFT means 2-(2,2,2-trifluoroethyl)-1-tetralone, PFP means 2-(2,2,3,3,3-Pentafluoropro-panoyl)-3,4-dihydronaphthalen-1(2H)-one and TPPO means phosphine oxide. The coordination of PVP and the rare earth complexes in solution was studied, and it was found that the fluorine atoms of the ligand had a significant impact on the aggregation-induced effect of the composites. The electron transitioned in the polymers and the complexes were enhanced greatly by the coordination. The colors of emission light could be adjusted by the coordination of the polymers and the rare earth complexes. Full article
(This article belongs to the Special Issue Electrospinning of Nanofibres)
Figures

Graphical abstract

Open AccessArticle Biocomposites Based on Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) (PHBHV) and Miscanthus giganteus Fibers with Improved Fiber/Matrix Interface
Polymers 2018, 10(5), 509; https://doi.org/10.3390/polym10050509
Received: 4 April 2018 / Revised: 27 April 2018 / Accepted: 30 April 2018 / Published: 7 May 2018
PDF Full-text (6915 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, green biocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and Miscanthus giganteus fibers (MIS) were prepared in the presence of dicumyl peroxide (DCP) via reactive extrusion. The objective of this study was to optimize the interfacial adhesion between the reinforcement and
[...] Read more.
In this paper, green biocomposites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and Miscanthus giganteus fibers (MIS) were prepared in the presence of dicumyl peroxide (DCP) via reactive extrusion. The objective of this study was to optimize the interfacial adhesion between the reinforcement and the matrix, improving the mechanical properties of the final material. To this aim, two fibers mass fractions (5 and 20 wt %) and two different fiber sizes obtained by two opening mesh sieves (1 mm and 45 μm) were investigated. The impregnation of fibers with DCP before processing was carried out in order to promote the PHBHV grafting onto MIS fibers during the process, favoring, in this way, the interfacial adhesion between fibers and matrix, instead of the crosslinking of the matrix. All composites were realized by extrusion and injection molding processing and then characterized by tensile tests, FTIR-ATR, SEM, DSC and XRD. According to the improved adhesion of fibers to matrix due to DCP, we carried out an implementation of models involving that can predict the effective mechanical properties of the biocomposites. Three phases were taken into account here: fibers, gel (crosslinked matrix), and matrix fractions. Due to the complexity of the system (matrix–crosslinked matrix–fibers) and to the lack of knowledge about all the phenomena occurring during the reactive extrusion, a mathematical approach was considered in order to obtain information about the modulus of the crosslinked matrix and its fraction in the composites. This study aims to estimate these last values, and to clarify the effect caused by the presence of vegetal fibers in a composite in which different reactions are promoted by DCP. Full article
(This article belongs to the Special Issue Modification of Natural Fibres to Improve Biocomposites Performances)
Figures

Graphical abstract

Open AccessArticle Phase Morphology of NR/SBR Blends: Effect of Curing Temperature and Curing Time
Polymers 2018, 10(5), 510; https://doi.org/10.3390/polym10050510
Received: 23 April 2018 / Revised: 3 May 2018 / Accepted: 4 May 2018 / Published: 8 May 2018
PDF Full-text (25391 KB) | HTML Full-text | XML Full-text
Abstract
The morphology of natural rubber/styrene–butadiene rubber blends (NR/SBR) was characterized by atomic force microscopy (AFM), with regard to curing temperature and curing time. The changes in blend morphology were directly visualized by AFM which confirmed the results of indirect experiments like differential scanning
[...] Read more.
The morphology of natural rubber/styrene–butadiene rubber blends (NR/SBR) was characterized by atomic force microscopy (AFM), with regard to curing temperature and curing time. The changes in blend morphology were directly visualized by AFM which confirmed the results of indirect experiments like differential scanning calorimetry (DSC). Comparing the phase morphologies at different curing temperatures indicated that the domain size of SBR increases with temperature at lower curing temperatures, but domain growing stops at the latest scorch time. This effect is explained by longer scorch times at low curing temperatures which facilitate phase separation, while the short scorch times at higher temperatures meant that the coalescence of SBR phases was hindered by cross-linking between polymer chains. Full article
(This article belongs to the Special Issue Elastomers)
Figures

Graphical abstract

Open AccessArticle Evaluation of the Stability of Polymeric Materials Exposed to Palm Biodiesel and Biodiesel–Organic Acid Blends
Polymers 2018, 10(5), 511; https://doi.org/10.3390/polym10050511
Received: 21 March 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 9 May 2018
PDF Full-text (7102 KB) | HTML Full-text | XML Full-text
Abstract
The aim of the present work is to evaluate the impact of pure palm biodiesel fuel (B100) and biodiesel blends with 0.32% oleic, palmitic, acetic, myristic, and stearic acids on the properties of some polymeric materials used commonly in the manufacture of auto
[...] Read more.
The aim of the present work is to evaluate the impact of pure palm biodiesel fuel (B100) and biodiesel blends with 0.32% oleic, palmitic, acetic, myristic, and stearic acids on the properties of some polymeric materials used commonly in the manufacture of auto parts such as the polyamide 66 (PA66), polyoxymethylene (POM), and high-density polyethylene (HDPE). The effects of the B100 and B100–acid blends on polymeric materials were examined by comparing changes in the gain/loss of mass and by measuring the hardness, the impact strength, and the tensile strength of the materials at the end of the exposure. The characterization of the polymers was carried out before and after exposure by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). After the immersion in B100–acids blends, the HDPE exhibited an increase in mass of 5%, which was very similar in all blends. The PA66 showed a small decrease in weight (2% approx.) in all mixtures. The POM presented an increase in the percentage of weight in the mixture of B100 with acetic acid of 0.3%. A decrease was observed in the crystallinity of the HDPE when exposed to blends of B100–acids. This behavior may be associated with a plasticizing effect in the HDPE exposed to the blends. The mechanical properties of POM and HDPE showed no significant changes after immersion in the fuels. On the other hand, PA66 exhibited a significant decrease in maximum stress value after immersion in B100, B100–oleic acid and B100–palmitic acid blends. The variation of the mechanical properties of the PA66 after exposure to B100 was potentiated by addition of organic acids. The assessed polymers did not undergo appreciable changes in the chemical structure of the samples after immersion in the fuels, so the variation in the mechanical properties could be explained by physical absorption of the fuel into the polymers. Full article
Figures

Graphical abstract

Open AccessArticle Study of theThermo-/pH-Sensitivity of Stereo-Controlled Poly(N-isopropylacrylamide-co-IAM) Copolymers via RAFT Polymerization
Polymers 2018, 10(5), 512; https://doi.org/10.3390/polym10050512
Received: 13 April 2018 / Revised: 5 May 2018 / Accepted: 6 May 2018 / Published: 9 May 2018
PDF Full-text (5859 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a smart copolymer, Poly(nipam-co-IAM) was synthesized by copolymerization of N-isopropylacrylamide (nipam) and itaconamic acid (IAM) through reversible addition-fragmentation chain-transfer (RAFT) polymerization. Poly(nipam-co-IAM) has been studied previously synthesized via radical polymerization without stereo-control, and this work used cumyl dithiobenzoate and
[...] Read more.
In this work, a smart copolymer, Poly(nipam-co-IAM) was synthesized by copolymerization of N-isopropylacrylamide (nipam) and itaconamic acid (IAM) through reversible addition-fragmentation chain-transfer (RAFT) polymerization. Poly(nipam-co-IAM) has been studied previously synthesized via radical polymerization without stereo-control, and this work used cumyl dithiobenzoate and Ytterbium(III) trifluoromethanesulfonate as RAFT and stereo-control agents, respectively. The stereo-control result in this work shows that tacticity affects the lower critical solution temperature (LCST) and/or the profile of phase separation of Poly(nipam-co-IAM). In the pH 7 and pH 10 buffer solutions, the P(nipam-co-IAM) copolymer solutions showed soluble–insoluble–soluble transitions, i.e., both LCST and upper critical solution temperature (UCST) transitions, which had not been found previously, and the insoluble to soluble transition (redissolved behavior) occurred at a relatively low temperature. The insoluble to soluble transition of P(nipam-co-IAM) in alkaline solution occurred at a temperature of less than 45 °C. However, the redissolved behavior of P(nipam-co-IAM) was found only in the pH 7 and pH 10 buffer solutions and this redissolved behavior was more prominent for the atactic copolymers than in the isotactic-rich ones. In addition, the LCST results under our experimental range of meso content did not show a significant difference between the isotactic-rich and the atactic P(nipam-co-IAM). Further study on the soluble-insoluble-soluble (S-I-S) transition and the application thereof for P(nipam-co-IAM) copolymers will be conducted. Full article
(This article belongs to the Special Issue RAFT Living Radical Polymerization and Self-Assembly)
Figures

Graphical abstract

Open AccessArticle Phospholipid-Coated Mesoporous Silica Nanoparticles Acting as Lubricating Drug Nanocarriers
Polymers 2018, 10(5), 513; https://doi.org/10.3390/polym10050513
Received: 7 April 2018 / Revised: 29 April 2018 / Accepted: 30 April 2018 / Published: 9 May 2018
PDF Full-text (8400 KB) | HTML Full-text | XML Full-text
Abstract
Osteoarthritis (OA) is a severe disease caused by wear and inflammation of joints. In this study, phospholipid-coated mesoporous silica nanoparticles (MSNs@lip) were prepared in order to treat OA at an early stage. The phospholipid layer has excellent lubrication capability in aqueous media due
[...] Read more.
Osteoarthritis (OA) is a severe disease caused by wear and inflammation of joints. In this study, phospholipid-coated mesoporous silica nanoparticles (MSNs@lip) were prepared in order to treat OA at an early stage. The phospholipid layer has excellent lubrication capability in aqueous media due to the hydration lubrication mechanism, while mesoporous silica nanoparticles (MSNs) act as effective drug nanocarriers. The MSNs@lip were characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectrum, X-ray photoelectron spectrum, thermogravimetric analysis and dynamic light scattering techniques to confirm that the phospholipid layer was coated onto the surface of MSNs successfully. A series of tribological tests were performed under different experimental conditions, and the results showed that MSNs@lip with multi-layers of phospholipids greatly reduced the friction coefficient in comparison with MSNs. Additionally, MSNs@lip demonstrated sustained drug release behavior and were biocompatible based on CCK-8 assay using MC3T3-E1 cells. The MSNs@lip developed in the present study, acting as effective lubricating drug nanocarriers, may represent a promising strategy to treat early stage OA by lubrication enhancement and drug delivery therapy. Full article
(This article belongs to the Special Issue Polymer Scaffolds for Biomedical Application)
Figures

Graphical abstract

Open AccessArticle In-Situ Incorporation of Alkyl-Grafted Silica into Waterborne Polyurethane with High Solid Content for Enhanced Physical Properties of Coatings
Polymers 2018, 10(5), 514; https://doi.org/10.3390/polym10050514
Received: 7 April 2018 / Revised: 3 May 2018 / Accepted: 8 May 2018 / Published: 9 May 2018
PDF Full-text (5224 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Waterborne polyurethane (WPU) with high solid content (45%) was obtained by utilizing dimethylol propionic acid (DMPA) and ethoxylated capped polymeric diol as complex hydrophilic groups. Alkyl-grafted silica was incorporated into polymer matrix through in situ polymerization to improve the performance of coatings casted
[...] Read more.
Waterborne polyurethane (WPU) with high solid content (45%) was obtained by utilizing dimethylol propionic acid (DMPA) and ethoxylated capped polymeric diol as complex hydrophilic groups. Alkyl-grafted silica was incorporated into polymer matrix through in situ polymerization to improve the performance of coatings casted from WPU dispersions. The addition of alkyl-grafted silica enlarged the particle size distribution whilst increased emulsion viscosity, which showed little influence on attainment of high solid content for WPU. The properties of obtained WPU/Silica coatings were investigated. Results showed that the functionalized surface of silica provides good compatibility with the WPU matrix, which promoted the homogeneous dispersion of silica particles. This facilitated the formation of nanosized silica papillae on coatings, contributing to surface roughness and hydrophobicity. Solvent resistance of WPU was enhanced with existence of alkyl-grafted silica particles. The WPU/Silica coatings also displayed improved thermal stability due to the thermal insulation ability and tortuous path effect of silica. Besides this, valid interactions between silica and WPU resulted in hybrid microphase of which the synergistic effect imparted superior mechanical properties at relatively low loadings of silica (2%). The facile technique presented here will provide an effective and promising method for preparing WPU hybrids with enhanced performance. Full article
(This article belongs to the Special Issue Polymer Hybrids and Composites)
Figures

Graphical abstract

Open AccessArticle Reactive Energetic Plasticizers Utilizing Cu-Free Azide-Alkyne 1,3-Dipolar Cycloaddition for In-Situ Preparation of Poly(THF-co-GAP)-Based Polyurethane Energetic Binders
Polymers 2018, 10(5), 516; https://doi.org/10.3390/polym10050516
Received: 14 April 2018 / Revised: 8 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
PDF Full-text (3538 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Reactive energetic plasticizers (REPs) coupled with hydroxy-telechelic poly(glycidyl azide-co-tetrahydrofuran) (PGT)-based energetic polyurethane (PU) binders for use in solid propellants and plastic-bonded explosives (PBXs) were investigated. The generation of gem-dinitro REPs along with a terminal alkyne stemmed from a series of
[...] Read more.
Reactive energetic plasticizers (REPs) coupled with hydroxy-telechelic poly(glycidyl azide-co-tetrahydrofuran) (PGT)-based energetic polyurethane (PU) binders for use in solid propellants and plastic-bonded explosives (PBXs) were investigated. The generation of gem-dinitro REPs along with a terminal alkyne stemmed from a series of finely designed approaches to not only satisfy common demands as conventional energetic plasticizers, but also to prevent the migration of plasticizers. The miscibility and rheological behavior of a binary mixture of PGT/REP with various REP fractions were quantitatively determined by differential scanning calorimetry (DSC) and rheometer, respectively, highlighting the promising performance of REPs in the formulation process. The kinetics on the distinct reactivity of propargyl vs. 3-butynyl species of REPs towards the azide group of the PGT prepolymer in terms of Cu-free azide-alkyne 1,3-dipolar cycloaddition (1,3-DPCA) was studied by monitoring 1H nuclear magnetic resonance spectroscopy and analyzing the activation energies (Ea) obtained using DSC. The thermal stability of the finally cured energetic binders with the incorporation of REPs indicated that the thermal stability of the REP/PGT-based PUs was maintained independently of the REP content. The tensile strength and modulus of the PUs increased with an increase in the REP content. In addition, the energetic performance and sensitivity of REP and REP triazole species was predicted. Full article
(This article belongs to the Special Issue Green Plasticizers for Polymers)
Figures

Graphical abstract

Open AccessArticle Diffractive and Interferometric Characterization of Nanostructured Photopolymer for Sharp Diffractive Optical Elements Recording
Polymers 2018, 10(5), 518; https://doi.org/10.3390/polym10050518
Received: 9 April 2018 / Revised: 27 April 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
PDF Full-text (5728 KB) | HTML Full-text | XML Full-text
Abstract
We study the behavior of a nanoparticle-polymer composite (NPC) material, based on a thiol-ene monomer system, working with long grating spacing. Thus, we evaluate the suitability of the NPC for storing complex diffractive optical elements with sharp profiles, such as blazed gratings. Using
[...] Read more.
We study the behavior of a nanoparticle-polymer composite (NPC) material, based on a thiol-ene monomer system, working with long grating spacing. Thus, we evaluate the suitability of the NPC for storing complex diffractive optical elements with sharp profiles, such as blazed gratings. Using holographic methods, we measure the “apparent” diffusion of the material and the influence of the spatial period on this diffusion. The applicability of this material in complex diffractive optical elements (DOEs) recording is analyzed using an interferometric method. Supported by the results of this analysis, we record blazed gratings with different grating spacing and measure the maximum diffraction efficiency (DE) achieved. The results show that NPC has a good behavior in this range of spatial frequencies. Full article
(This article belongs to the Special Issue Holographic Materials and Photonic Applications)
Figures

Graphical abstract

Open AccessArticle PLGA Microspheres Loaded with β-Cyclodextrin Complexes of Epigallocatechin-3-Gallate for the Anti-Inflammatory Properties in Activated Microglial Cells
Polymers 2018, 10(5), 519; https://doi.org/10.3390/polym10050519
Received: 4 March 2018 / Revised: 6 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
PDF Full-text (2666 KB) | HTML Full-text | XML Full-text
Abstract
Although epigallocatechin-3-gallate (EG) is well-known as a potent antioxidant and free radical scavenger for neurodegenerative diseases, it still has disadvantages that reduce its treatment effectiveness due to low bioavailability, slow absorption, and water solubility. Therefore, the aim of this study is to improve
[...] Read more.
Although epigallocatechin-3-gallate (EG) is well-known as a potent antioxidant and free radical scavenger for neurodegenerative diseases, it still has disadvantages that reduce its treatment effectiveness due to low bioavailability, slow absorption, and water solubility. Therefore, the aim of this study is to improve the bioavailability of EG and increase the effectiveness of anti-inflammatory properties to microglial cells by using Poly(Lactide-co-Glycolide) (PLGA) microspheres as carriers. In this study, we used UV–Vis spectroscopy to show the formation of the complex of β-cyclodextrin (β-CD) and EG (CD-EG). The loading efficiency of EG in PLGA microspheres was optimized by the addition of β-CD. The highest loading efficiency of 16.34% was found among other formulations. The results of Fourier transform infrared spectroscopy indicated the loading of CD-EG in PLGA microspheres. The scanning electron microscopic images demonstrated the spherical PLGA particles with controlled particles size ranging from 1–14 µm. Moreover, the in vitro release of EG was conducted to explore the sustained release property of the PLGA formulations. In the in vitro model of mouse microglial cells (BV-2 cells) stimulated by lipopolysaccharide, the cytotoxicity test showed that for up to 1 mg/mL of PLGA microspheres no toxicity to BV-2 cells was found. PLGA microspheres can significantly suppress the nitric oxide production from BV-2 cells, indicating EG loaded in PLGA microspheres can suppress the inflammation of activated microglial cells. Furthermore, the intracellular iNOS in BV-2 cells was also found to be down regulated. In summary, we have successfully shown that the use of β-CD can increase the loading efficiency of EG in PLGA microspheres and provide neuroprotective effect on the activated microglial cells. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
Figures

Graphical abstract

Open AccessArticle Synthesis of Zirconium-Containing Polyhedral Oligometallasilsesquioxane as an Efficient Thermal Stabilizer for Silicone Rubber
Polymers 2018, 10(5), 520; https://doi.org/10.3390/polym10050520
Received: 16 April 2018 / Revised: 8 May 2018 / Accepted: 10 May 2018 / Published: 11 May 2018
PDF Full-text (30860 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Free radicals play a negative role during the thermal degradation of silicone rubber (SR). Quenching free radicals is proposed to be an efficient way to improve the thermal-oxidative stability of SR. In this work, a novel zirconium-containing polyhedral oligometallasilsesquioxane (Zr-POSS) with free-radical quenching
[...] Read more.
Free radicals play a negative role during the thermal degradation of silicone rubber (SR). Quenching free radicals is proposed to be an efficient way to improve the thermal-oxidative stability of SR. In this work, a novel zirconium-containing polyhedral oligometallasilsesquioxane (Zr-POSS) with free-radical quenching capability was synthesized and characterized. The incorporation of Zr-POSS effectively improved the thermal-oxidative stability of SR. The T5 (temperature at 5% weight loss) of SR/Zr-POSS significantly increased by 31.7 °C when compared to the unmodified SR. Notably, after aging 12 h at 280 °C, SR/Zr-POSS was still retaining about 65%, 60%, 75%, and 100% of the tensile strength, tear strength, elongation at break, and hardness before aging, respectively, while the mechanical properties of the unmodified SR were significantly decreased. The possible mechanism of Zr-POSS for improving the thermal-oxidative stability of SR was intensively studied and it was revealed that the POSS structure could act as a limiting point to suppress the random scission reaction of backbone. Furthermore, Zr could quench the free radicals by its empty orbital and transformation of valence states. Therefore, it effectively suppressed the thermal-oxidative degradation and crosslinking reaction of the side chains. Full article
(This article belongs to the Special Issue Thermal Properties and Applications of Polymers)
Figures

Graphical abstract

Open AccessArticle Polyhexamethylene Biguanide and Nadifloxacin Self-Assembled Nanoparticles: Antimicrobial Effects against Intracellular Methicillin-Resistant Staphylococcus aureus
Polymers 2018, 10(5), 521; https://doi.org/10.3390/polym10050521
Received: 24 March 2018 / Revised: 29 April 2018 / Accepted: 9 May 2018 / Published: 12 May 2018
PDF Full-text (3029 KB) | HTML Full-text | XML Full-text
Abstract
The treatment of skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge, partly due to localization of the bacteria inside the host’s cells, where antimicrobial penetration and efficacy is limited. We formulated the cationic polymer polyhexamethylene biguanide (PHMB)
[...] Read more.
The treatment of skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge, partly due to localization of the bacteria inside the host’s cells, where antimicrobial penetration and efficacy is limited. We formulated the cationic polymer polyhexamethylene biguanide (PHMB) with the topical antibiotic nadifloxacin and tested the activities against intracellular MRSA in infected keratinocytes. The PHMB/nadifloxacin nanoparticles displayed a size of 291.3 ± 89.6 nm, polydispersity index of 0.35 ± 0.04, zeta potential of +20.2 ± 4.8 mV, and drug encapsulation efficiency of 58.25 ± 3.4%. The nanoparticles killed intracellular MRSA, and relative to free polymer or drugs used separately or together, the nanoparticles displayed reduced toxicity and improved host cell recovery. Together, these findings show that PHMB/nadifloxacin nanoparticles are effective against intracellular bacteria and could be further developed for the treatment of skin and soft tissue infections. Full article
(This article belongs to the Special Issue Antimicrobial Polymers)
Figures

Graphical abstract

Open AccessArticle Degradation of Silicone Rubbers as Sealing Materials for Proton Exchange Membrane Fuel Cells under Temperature Cycling
Polymers 2018, 10(5), 522; https://doi.org/10.3390/polym10050522
Received: 12 April 2018 / Revised: 4 May 2018 / Accepted: 10 May 2018 / Published: 13 May 2018
PDF Full-text (2999 KB) | HTML Full-text | XML Full-text
Abstract
Gaskets are compressed in proton exchange membrane fuel cells (PEMFCs) to keep fuel, oxidant and coolant within their respective regions and are very important for sealing and maintaining electrochemical performance of fuel cells during their long-term operation. It has been proved that the
[...] Read more.
Gaskets are compressed in proton exchange membrane fuel cells (PEMFCs) to keep fuel, oxidant and coolant within their respective regions and are very important for sealing and maintaining electrochemical performance of fuel cells during their long-term operation. It has been proved that the gas leakage caused by the failure of the gaskets following long-term operation is one of the main reasons for PEMFC performance degradation. In this work, degradation of silicone rubbers, the potential gasket materials for PEMFCs, were investigated in the simulated PEMFC environment solution, weak acid solution, de-ionized water and air, respectively, under alternating temperature cycling from −20 °C to 90 °C. The changes in hardness, weight, chemical properties, mechanical behavior and surface morphology of the samples of silicone rubbers were studied after a certain number of temperature cycles. The results show that with the increase in temperature cycles, the hardness of the samples increases and the weight of the samples decreases gradually. Scanning electron microscopy reveals that cracks and caves constantly appear on the surface of the samples. Attenuated total reflection Fourier transform infrared spectra (ATR-FTIR) results demonstrate that the surface chemistry changes via de-crosslinking and chain scission in the backbone due to the exposure of samples to the environments over time under alternating temperature cycles. Full article
(This article belongs to the Special Issue Polymeric Materials for Electrochemical Energy Conversion and Storage)
Figures

Graphical abstract

Open AccessArticle Preparation and Evaluation of Coal Fly Ash/Chitosan Composites as Magnetic Supports for Highly Efficient Cellulase Immobilization and Cellulose Bioconversion
Polymers 2018, 10(5), 523; https://doi.org/10.3390/polym10050523
Received: 17 April 2018 / Revised: 9 May 2018 / Accepted: 11 May 2018 / Published: 14 May 2018
PDF Full-text (3538 KB) | HTML Full-text | XML Full-text
Abstract
Two magnetic supports with different morphologies and particle sizes were designed and prepared for cellulase immobilization based on chitosan and industrial by-product magnetic coal fly ash (MCFA). One was prepared by coating chitosan onto spherical MCFA particles to form non-porous MCFA@chitosan gel microcomposites
[...] Read more.
Two magnetic supports with different morphologies and particle sizes were designed and prepared for cellulase immobilization based on chitosan and industrial by-product magnetic coal fly ash (MCFA). One was prepared by coating chitosan onto spherical MCFA particles to form non-porous MCFA@chitosan gel microcomposites (Support I) with a size of several micrometers, and the other was prepared using the suspension method to form porous MCFA/chitosan gel beads (Support II) with a size of several hundred micrometers. Cellulase was covalent binding to the support by glutaraldehyde activation method. The morphology, structure and magnetic property of immobilized cellulase were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and a vibrating-sample magnetometer. The cellulase loading on Support I was 85.8 mg/g with a relatlvely high activity recovery of 76.6%, but the immobilized cellulase exhibited low thermal stability. The cellulase loading on Support II was 76.8 mg/g with a relative low activity recovery of 51.9%, but the immobilized cellulase showed high thermal stability. Cellulase immobilized on Support I had a glucose productivity of 219.8 mg glucose/g CMC and remained 69.9% of the original after 10 cycles; whereas the glucose productivity was 246.4 mg glucose/g CMC and kept 75.5% of its initial value after 10 repeated uses for Support II immobilized cellulase. The results indicate that the two supports can be used as cheap and effective supports to immobilize enzymes. Full article
(This article belongs to the Special Issue Renewable Polymer Composites)
Figures

Figure 1

Open AccessArticle Comparison of Candida antarctica Lipase B Variants for Conversion of ε-Caprolactone in Aqueous Medium—Part 2
Polymers 2018, 10(5), 524; https://doi.org/10.3390/polym10050524
Received: 10 April 2018 / Revised: 26 April 2018 / Accepted: 10 May 2018 / Published: 14 May 2018
PDF Full-text (7164 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Enzyme-catalyzed ring-opening polymerization of lactones is a method of increasing interest for the synthesis of polyesters. In the present work, we investigated which changes in the structure of Candida antarctica lipase B (CaLB) shift the catalytic equilibrium between esterification and hydrolysis towards polymerization.
[...] Read more.
Enzyme-catalyzed ring-opening polymerization of lactones is a method of increasing interest for the synthesis of polyesters. In the present work, we investigated which changes in the structure of Candida antarctica lipase B (CaLB) shift the catalytic equilibrium between esterification and hydrolysis towards polymerization. Therefore, we present two concepts: (i) removing the glycosylation of CaLB to increase the surface hydrophobicity; and (ii) introducing a hydrophobic lid adapted from Pseudomonas cepacia lipase (PsCL) to enhance the interaction of a growing polymer chain to the elongated lid helix. The deglycosylated CaLB (CaLB-degl) was successfully generated by site-saturation mutagenesis of asparagine 74. Furthermore, computational modeling showed that the introduction of a lid helix at position Ala148 was structurally feasible and the geometry of the active site remained intact. Via overlap extension PCR the lid was successfully inserted, and the variant was produced in large scale in Pichia pastoris with glycosylation (CaLB-lid) and without (CaLB-degl-lid). While the lid variants show a minor positive effect on the polymerization activity, CaLB-degl showed a clearly reduced hydrolytic and enhanced polymerization activity. Immobilization in a hydrophobic polyglycidol-based microgel intensified this effect such that a higher polymerization activity was achieved, compared to the “gold standard” Novozym® 435. Full article
Figures

Graphical abstract

Open AccessArticle Modeling the Viscoelastic Hysteresis of Dielectric Elastomer Actuators with a Modified Rate-Dependent Prandtl–Ishlinskii Model
Polymers 2018, 10(5), 525; https://doi.org/10.3390/polym10050525
Received: 23 March 2018 / Revised: 11 May 2018 / Accepted: 12 May 2018 / Published: 14 May 2018
PDF Full-text (2952 KB) | HTML Full-text | XML Full-text
Abstract
Dielectric elastomer actuators (DEAs) are known as a type of electric-driven artificial muscle that have shown promising potential in the field of soft robotics. However, the inherent viscoelastic nonlinearity makes the modeling and control of DEAs challenging. In this paper, we propose a
[...] Read more.
Dielectric elastomer actuators (DEAs) are known as a type of electric-driven artificial muscle that have shown promising potential in the field of soft robotics. However, the inherent viscoelastic nonlinearity makes the modeling and control of DEAs challenging. In this paper, we propose a new phenomenological modeling approach with the Prandtl–Ishlinskii (P–I) model to characterize the viscoelastic hysteresis nonlinearity of DEAs. Differently from the commonly used physics-based models, the developed phenomenological model, called the modified rate-dependent P–I model (MRPIM), produces behavior similar to that of physics-based models but without necessarily considering physical insight into the modeling problem. In this way, the developed MRPIM can characterize the asymmetric and rate-dependent viscoelastic hysteresis with a relative simple mathematical format using only the experimental data. To validate the development, experimental tests were conducted with seven different frequencies; four were selected to identify the model parameters and the rest of the data were used to further verify the model. Comparisons between the model prediction and experimental data demonstrate that the MRPIM can precisely describe the viscoelastic hysteresis effect of DEAs with a maximum prediction error of 9.03% and root-mean-square prediction error of 4.50%. Full article
(This article belongs to the Special Issue Soft Materials and Systems)
Figures

Graphical abstract